Users of Lua SWIM module likely will use Lua objects as a
payload. Lua objects are serialized into MessagePack
automatically, and deserialized back on other instances. But
deserialization of 1.2Kb payload on each member:payload()
invocation is quite heavy operation. This commit caches decoded
payloads to return them again until change.

A microbenchmark showed, that cached payload is returned ~100
times faster, than it is decoded each time. Even though a tested
payload was quite small and simple:

    s:set_payload({a = 100, b = 200})

Even this payload is returned 100 times faster, and does not
affect GC.

Part of #3234

Sometimes, especially in tests, it is useful to make something
like this:

    s:add_member({uuid = member:uuid(), uri = member:uri()})

But member:uuid() is cdata struct tt_uuid. This commit allows
that.

Part of #3234

Expose iterators API to be able to iterate over a member table in
a 'for' loop like it would just be a Lua table.

Part of #3234

Expose API to search members by UUID, to read their attributes,
to set payload.

Part of #3234

Expose methods to add, remove, probe members by uri, uuid. Expose
broadcast method to probe multiple members by port.

Part of #3234

SWIM as a library can be useful not only for server internals,
but for users as well. This commit exposes Lua bindings to SWIM
C API. Here only basic bindings are introduced to create, delete,
quit, check a SWIM instance. With sanity tests.

Part of #3234

Similar methods validate their arguments: add_member,
remove_member. Validate here as well for consistency.

Part of #3234

Firstly, I thought that there is an error - swim_begin_step()
does not reschedules round timer, when new_round() fails. But
then new_round() appeared never failing. This commit makes it
void to eliminate confusion.

Probably it is a legacy since the shuffled members array was
allocated and freed in new_round().

Part of #3234

Appeared, that libev does not allow to change ev_timer values in
flight. A timer, reset via ev_timer_set(), should be restarted,
because the function changes 'ev_timer.at', which in turn is used
internally by timer routines.

Part of #3234

Lua, which suffers from lack of ability to pass values by
pointers into FFI functions, nor has an address operator '&' to
take an address of integer or char or anything. Because of that
a user need to either use ffi.new(type[1]) or use static buffer,
but for such small allocations they are both too expensive and
aggravate GC problem.

Now buffer module provides preallocated basic types to use in FFI
functions. The commit is motivated by one another place where
ffi.new('int[1]') appeared, in SWIM module, to obtain payload
size as an out parameter of a C function.

Static allocator gives memory blocks from cyclic BSS memory
block of 3 pages 4096 bytes each. It is much faster than
malloc, when a temporary buffer is needed. Moreover, it does not
complicate GC job. Despite being faster than malloc, it is still
slower, than ffi.new() of size <= 128 known in advance (according
to microbenchmarks).

ffi.new(size<=128) works either much faster or with the same
speed as static_alloc, because internally FFI allocator library
caches small blocks and can return them without malloc().

A simple micro benchmark showed, that ffi.new() vs
buffer.static_alloc() is ~100 times slower on allocations of
> 128 size,  on <= 128 when size is not inlined.

To better understand what is meant as 'inlined': this

    ffi.new('char[?]', < <=128 >)

works ~100 times faster than this:

    local size = <= 128
    ffi.new('char[?]', size)

ffi.new() with inlined size <= 128 works faster than light, and
even static allocator can't beat it.

Certain kinds of DML requests don't update secondary indexes, e.g.
UPDATE that doesn't touch secondary index parts or DELETE for which
generation of secondary index statements is deferred. For such a request
vy_is_committed(env, space) may return false on recovery even if it has
actually been dumped: since such a statement is not dumped for secondary
indexes, secondary index's vy_lsm::dump_lsn may be less than such
statement's signature, which makes vy_is_committed() assume that the
statement hasn't been dumped. Further in the code we have checks that
ensure that if we execute a request on recovery, it must not be dumped
for the primary index (as the primary index is always dumped after
secondary indexes for the sake of recovery), which fires in this case.

To fix that, let's refactor the code basing on the following two facts:
 - Primary index is always updated by a DML request.
 - Primary index may only be dumped after secondary indexes.

Closes #4222

Yet another fix for building of small library as part of tarantool.
Before this commit slab_arena test fails:

 | [019] Test failed! Result content mismatch:
 | [019] --- small/slab_arena.result	Mon May 20 21:37:46 2019
 | [019] +++ small/slab_arena.reject	Mon May 20 21:47:01 2019
 | [019] @@ -23,3 +23,4 @@
 | [019]  arena->maxalloc = 2000896
 | [019]  arena->used = 0
 | [019]  arena->slab_size = 65536
 | [019] +ERROR: Expected dd flag on VMA address 0x7f3ec2080000

See the corresponding commit in the small submdoule for more info.

The autoincrement code was written when there were no nested field.
Now, it isn't enough to just skip to the autoincrement field - we also
need to descend deeper if key_part->path is set.

Note, the code expects the nested field to be present and set to NULL.
That is, if field path is [1].a.b, the tuple must have all intermediate
fields set: {{a = {b = box.NULL}}} (usage of box.NULL is mandatory to
create a tuple like that in Lua).

Closes #4210

Closes #4009

@TarantoolBot document
Title: Sequence can now be set for an index part other than the first

Initially one could attach a sequence (aka autoincrement) only to the
first index part. Now it's possible to attach a sequence to any primary
index part. The part still must be integer though.

Syntax:

```
box.schema.space.create('test')
box.space.test:create_index('primary', {
    parts = {{1, 'string'}, {2, 'unsigned'}, {3, 'unsigned'}},
    sequence = true, sequence_part = 2
})
box.space.test:insert{'a', box.null, 1} -- inserts {'a', 1, 1}
```

Note, `sequence_part` option is 1-base.

If `sequence_part` is omitted, 1 is used, which assures backward
compatibility with the original behavior.

One can also attach a sequence to another index part using
`index.alter` (the code below continues the example above):

```
box.space.test.index.primary:alter{sequence_part = 3}
box.space.test:insert{'a', 1, box.null, 'x'} -- inserts {'a', 1, 2, 'x'}
```

A check was missing in index.alter. This resulted in an attempt to drop
the sequence attached to the altered index even if the sequence was not
modified.

Closes #4214

When schema.lua was introduced, there was no such thing as space format
and we had to access tuple fields by no. Now we can use human readable
names. Let's do it - this should improve code readability.

A note about box/alter.test.lua: for some reason it clears format of
_space and _index system spaces, which apparently breaks our assumption
about field names. Let's zap those pointless test cases.

Updated small submodule with the corresponding fix.

Background. Coio provides a way to schedule arbitrary tasks
execution in worker threads. A task consists of a function to
execute, and a custom destructor.

To push a task the function coio_task_post(task, timeout) was
used. When the function returns 0, a caller can obtain a result
and should free the task manually. But the trick is that if
timeout was 0, the task was posted in a detached state. A
detached task frees its memory automatically despite
coio_task_post() result, and does not even yield. Such a task
object can't be accessed and so much the more freed manually.

coio_getaddrinfo() used coio_task_post() and freed the task when
the latter function returned 0. It led to double free when
timeout was set 0. The bug was introduced here
800cec73 in an attempt to do not
yield in say_logrotate, because it is not fiber-safe.

Now there are two functions: coio_task_execute(task, timeout),
which never detaches a task completed successfully, and
coio_task_post(task), which posts a task in a detached state.

Closes #4209

According to the standard by Open Group, getaddrinfo() hints
argument is optional - it can be NULL. When it is NULL, hints
is assumed to have 0 in ai_flags, ai_socktype, and ai_protocol;
AF_UNSPEC in ai_family.

See The Open Group Base Specifications.

The result file of the test app-tap/init_script.test.lua was not updated
in 549140b3 ('box/memtx: Allow to skip
tuple memory from coredump').

Follow up #3509.

Made fixes:

- Added CMAKE_EXTRA_PARAMS environment to docker's container
  runs to enable -DENABLE_LTO=ON/OFF cmake option.

- Added CC/CXX environment to docker's container runs to set
  clang for cmake. Also the additional environment variables
  {CC,CXX}_FOR_BUILD were postponed, because we didn't
  run cross-compilation at the moment, for more info check:

    https://docs.travis-ci.com/user/languages/cpp/#choosing-compilers-to-test-against

- Changed LTO docker's image to 'debian-buster' due to LTO needed
  higher versions of packages, check for more information commit:

    f9e28ce4 ('Add LTO support')

- Fixed sources to avoid of failures on builds by GCC with LTO:

1)  src/box/memtx_rtree.c: In function ‘mp_decode_rect’:
    src/box/memtx_rtree.c:86:24: error: ‘c’ may be used uninitialized
      in this function [-Werror=maybe-uninitialized]
        rect->coords[i * 2] = c;
                            ^
    src/box/memtx_rtree.c:74:10: note: ‘c’ was declared here
      coord_t c;
              ^

2)  src/box/sql/func.c: In function ‘quoteFunc’:
    src/box/sql/func.c:1103:3: error: ‘b’ may be used uninitialized
      in this function [-Werror=maybe-uninitialized]
       sql_result_text(context, sql_value_boolean(argv[0]) ?
       ^
    src/box/sql/vdbeapi.c:217:7: note: ‘b’ was declared here
      bool b;
           ^

3)  src/box/tuple_update.c: In function ‘update_read_ops’:
    src/box/tuple_update.c:1022:4: error: ‘field_no’ may be used
      uninitialized in this function [-Werror=maybe-uninitialized]
        diag_set(ClientError, ER_NO_SUCH_FIELD_NO, field_no);
        ^
    src/box/tuple_update.c:1014:11: note: ‘field_no’ was declared here
       int32_t field_no;
               ^

4)  src/httpc.c: In function ‘httpc_set_verbose’:
    src/httpc.c:267:2: error: call to ‘_curl_easy_setopt_err_long’
      declared with attribute warning: curl_easy_setopt expects a long
      argument for this option [-Werror]
      curl_easy_setopt(req->curl_request.easy, CURLOPT_VERBOSE, curl_verbose);
      ^

5)  src/lua/httpc.c: In function ‘luaT_httpc_request’:
    src/lua/httpc.c:128:64: error: ‘MEM[(int *)&parser + 20B]’ may be used
      uninitialized in this function [-Werror=maybe-uninitialized]
      lua_pushinteger(L, (parser.http_minor > 0) ? parser.http_minor: 0);
                                                                    ^
    src/lua/httpc.c:67:21: note: ‘MEM[(int *)&parser + 20B]’ was declared here
      struct http_parser parser;
                         ^
    src/lua/httpc.c:124:64: error: ‘MEM[(int *)&parser + 16B]’ may be used
      uninitialized in this function [-Werror=maybe-uninitialized]
      lua_pushinteger(L, (parser.http_major > 0) ? parser.http_major: 0);
                                                                    ^
    src/lua/httpc.c:67:21: note: ‘MEM[(int *)&parser + 16B]’ was declared here
      struct http_parser parser;
                         ^

Close #4215

In case if there are huge amount of tuples the whole
memory goes to coredump file even if we don't need it
for problem investigation. In result coredump may
blow up to gigabytes in size.

Lets allow to exclude this memory from dumping via
box.cfg::strip_core boolean parameter.

Note that the tuple's arena is used not only for tuples
themselves but for memtx->index_extent_pool and
memtx->iterator_pool as well, so they are affected
too.

Fixes #3509

@TarantoolBot document
Title: Document box.cfg.strip_core

When Tarantool runs under a heavy load the memory allocated
for tuples may be very huge in size and to eliminate this
memory from being present in `coredump` file the `box.cfg.strip_core`
parameter should be set to `true`.

The default value is `false`.

Negative size led to an assertion. The commit adds a check if
size is negative.

Closes #4224

box_process_join() and box_process_subscribe() use coio_write_xrow(),
which calls coio_writev_timeout() under hood. If a socket will block at
write() the function calls ev_io_start() to wake the fiber up when the
socket will be ready to write. This code assumes that the watcher
(struct ev_io) is initialized as coio watcher, i.e. coio_create() has
been called.

The reason why the code works before is that coio_write_xrow() in
box_process_{join,subscribe}() writes a small piece of data and so the
situation when a socket write buffer has less free space then needed is
rare.

Fixes #4110.

This patch replaces schema_find_id() with box_space_id_by_name()
in SQL. The box_space_id_by_name() is more specialized. In
addition, it checks if the user has sufficient rights, unlike
schema_find_id().

Closes #3570

This patch stops the parser if any error occurs. Prior to this
patch, it was possible to replace the error with another one,
since the parser may continue to work, even if an error occurred.

For example:
box.execute("insert into not_exist values(1) a")

The first error is "Space 'NOT_EXIST' does not exist", but "Syntax
error near 'a'" is displayed.

After this patch, the first error will be displayed.

Closes #3964
Closes #4195

Fixes #4194.

As we enforced applier row order so we don't need to reacquire schema
latch after a ddl statement.

Followup for: 056deb2c

Support more then 60 parallel jobs (#82, PR #171).

crypto.lua is a public module using OpenSSL directly. But now
lib/crypto encapsulates OpenSSL with additional checks and
similar but more conforming API. It allows to replace OpenSSL
cipher in crypto.lua with lib/crypto methods.

OpenSSL API is quite complex and hard to follow, additionally it
is very unstable. Encoding/decoding via OpenSSL methods usually
consists of multiple calls of a lot of functions. This patch
wraps OpenSSL API with one more easy to use and conforming
Tarantool code style in scope of crypto library.

The traditional OpenSSL API is wrapped as well in a form of
crypto_stream object, so OpenSSL API is not cut off.

Besides struct crypto_stream the library provides struct
crypto_codec which encapsulates all the steps of encryption logic
in two short functions:

    crypto_codec_encrypt/decrypt(iv, in, in_size, out, out_size)

A caller can create a needed codec via crypto_codec_new, which
now supports all the same algorithms as crypto.lua module.

Needed for #3234

Tarantool has a strict rule for naming methods of libraries - use
the library name as a prefix. For crypto lib methods it should be
'crypto_', not 'tnt_'.

Crypto in Tarantool core was implemented and used very poorly
uintil now. It was just a one tiny file with one-line wrappers
around OpenSSL API. Despite being small and simple, it provided a
powerful interface to the Lua land used by Lua 'crypto' public
and documented module.

Now the time comes when OpenSSL crypto features are wanted on
lower level and with richer API, in core library SWIM written
in C. This patch moves crypto wrappers into a separate library
in src/lib, and drops some methods from the header file because
they are never used from C, and are needed for exporting only.

Needed for #3234

msgpack.decode() internally uses 'const char *' variable to
decode msgpack, but somewhy expects only 'char *' as input.
This commit allows to pass 'const char *' as well.

Before the patch msgpack Lua module provided a method encode()
able to take a custom buffer to encode into. But it should be of
type 'struct ibuf', what made it impossible to use
buffer.IBUF_SHARED as a buffer, because its type is
'struct ibuf *'. Strangely, but FFI can't convert these types
automatically.

This commit allows to use 'struct ibuf *' as well, and moves this
functionality into a function in utils.h. Now both msgpack and
merger modules can use ibuf directly and by pointer.

swim_quit() notifies all the members that this instance has left
the cluster. Strangely, except self. It is not a real bug, but
showing 'left' status in self struct swim_member would be more
correct than 'alive', obviously.

It is possible, that self struct swim_member was referenced by a
user - this is how 'self' can be available after SWIM instance
deletion.

Part of #3234

SWIM internally tries to avoid unnecessary close+socket+bind
calls on reconfiguration if a new URI is the same as an old one.
SWIM transport compares <IP, port> couples and if they are
equal, does nothing.

But if a port is 0, it is not a real port, but a sign to the
kernel to find any free port on the IP address. In such a case
SWIM transport after bind() retrieves and saves a real port.

When the same URI is specified again, the transport compares two
addresses: old <IP, auto found port>, new <IP, 0>, sees they are
'different', and rebinds. It is not necessary, obviously, because
the new URI covers the old one.

This commit avoids rebind, when new IP == old IP, and new port is
0.

Part of #3234