A previous commit added reason details as error fields. But error
objects are serialized as strings by default thus loosing all the
details.

This commit makes ER_READONLY message contain the reason why it
happened in a human-readable form. That way it will be well
visible in the logs at least.

Follow-up #5568

ER_READONLY used not to have any details about the exact reason
why the instance is read-only. The patch changes that by adding
new fields into the error which explain why the error happened and
even help to avoid it for next requests.

Now from the error object can tell whether it was raised because
of box.cfg.read_only = true, or the instance is an orphan, or it
has election enabled but is not a leader, or the transaction limbo
belongs to another instance.

The alternative to ClientError alteration via error_payload was
not to touch struct error and introduce a new error type
specifically for ER_READONLY via a new C++ class like
ReadOnlyError. But it had drawbacks:

- There may be clients who expect ER_READONLY to have ClientError
  type. For instance, they check err.code == ER_READONLY only for
  err.type == 'ClientError';

- Having to introduce a new C++ class each time when want to add a
  new field into an error has to end. Rather sooner than later.

Closes #5568

@TarantoolBot document
Title: box.error.READONLY new attributes

Users could see the error code as `box.error.READONLY` in `.code`
field of an error object. The error didn't have any other
attributes except common ones like 'type'.

Now from the `box.error.READONLY` error users can see why it
happened. The reasons can be the following:

* The instance has `box.cfg.read_only = true`. Then the `READONLY`
error has at least these fields:
```
tarantool> err:unpack()
---
- reason: config
  code: 7
  type: ClientError
...
```

* The instance is an orphan. It enters that state if number of
connected replicas is < `box.cfg.replication_connect_quorum`. Then
`READONLY` error has at least these fields:
```
tarantool> err:unpack()
---
- reason: orphan
  code: 7
  type: ClientError
...
```

* The synchro queue has an owner which is not the given instance.
It usually happens if synchronous replication is used and there is
another instance who called `box.ctl.promote()`. Then `READONLY`
error has at least these fields:
```
tarantool> err:unpack()
---
- queue_owner_id: <box.info.id of the queue owner>
  queue_owner_uuid: <box.info.uuid of the queue owner>
  reason: synchro
  term: <last known box.info.election.term of the owner>
  code: 7
  type: ClientError
...
```
Note than `queue_owner_uuid` sometimes might be not present.

* The instance has `box.cfg.election_mode` not `off` and it is not
a leader. Then `READONLY` error has at least these fields:
```
tarantool> err:unpack()
---
- state: <box.info.election.state of this instance>
  leader_id: <box.info.id of the leader>
  leader_uuid: <box.info.uuid of the leader>
  reason: election
  term: <box.info.election.term of this instance>
  code: 7
  type: ClientError
...
```
`leader_id` and `leader_uuid` might be absent if the leader is not
known. For example, an election is still in progress. Note, than
`leader_uuid` sometimes might be not present even if `leader_id`
is.

If multiple reasons are true at the same time, then only one is
returned in the following order of preference: election, synchro,
config, orphan.

-- Wait until the instance becomes an elected leader.
server:wait_election_leader()

-- Wait until an election leader is found.
server:wait_election_leader_found()

-- Get numeric ID of the instance like in box.info.id.
server:instance_id()

-- Get UUID of the instance like in box.info.uuid.
server:instance_uuid()

These are going to be used in a new test in a next commit.

It takes box.cfg config as an argument. And changes the argument
by adding a new key 'command'. If the caller wants to pass the
same box.cfg or slightly modified to several build_server() calls,
it won't work - all options will be the same on all instances.

For example:

    local cfg = {...}
    cfg.replication = {url1}
    cluster:build_server(cfg)
    cfg.replication = {url2}
    cluster:build_server(cfg)

It will not work. Both servers will get the same 'command' and the
same 'replication'.

In Lua struct error used RTTI to return members of the error
depending on its type. If a field was added to error's payload, it
wasn't visible. The patch makes Lua use error_payload instead of
RTTI. Now if the payload gets a new field, it becomes
automatically visible in Lua without need to introduce a new
method for it.

Part of #5568
Part of #4610
Part of #4907

Before this patch mp_error API could only encode and decode
hardcoded fields from the C++ classes inheriting struct error.

The fields are gone from the classes in a previous patch - moved
into error_payload. Now to be able to support arbitrary fields in
the payload the MessagePack encoding/decoding must use its content
instead of hardcoded fields depending on error type.

Part of #5568
Part of #4610
Part of #4907

error_payload is a part of struct error now. All the fields stored
in C++ classes on top of struct error are moved into the payload.

Part of #5568
Part of #4610
Part of #4907

All optional fields soon will be moved into error_payload. Code
was optional too. But it is needed too often, the most used field.
The patch moves it into struct error to make it more accessible.

Also in future it should allow to drop the hack
ClientError::get_errcode() which tries to return error code
depending on error type. But could just store the code right away.

As a consequence of the patch, errors which didn't have an error
code at all before, such as LuajitError, now have it 0 in Lua.

Part of #5568
Part of #4610

It is a dictionary-like struct which stores keys with binary data
values. The values are supposed to be arbitrary MessagePack blobs:
number, string, bool, UUID, array, map, anything.

The payload is an array inside instead of a hash table because
number of keys will be <= 3 in all cases. And even when it will be
public, it is very unlikely it will be bigger.

Object of error_payload in a future patch will be stored in struct
error and will allow to extend it dynamically with more members.

This in turn is needed to extend ER_READONLY error with more
details about why it happened.

Part of #5568
Part of #4907

libuuid used to be a separate library since
de11d68a ("CMake: refactor
dependencies of internal libraries").

Unclear what was it done for. The commit says "fir unit tests".
But they perfectly fine can depend on libcore like many of them
do already.

Because of libuuid being a separate library, libcore can't use
tt_uuid, because that would be a cyclic dependency. And that won't
allow to introduce tt_uuid-dependent API in a next patch.

Hence libuuid is merged into libcore.

Needed for #5568

And from diag_add(). This will be helpful not to bother with
box_error_last() and diag_last_error(diag_get()) in the future
patch. It will change some attributes of a just created
ER_READONLY error to add more details.

Part of #5568

Watcher unit test linked with libbox and included
core_test_utils.c. Both contain cord_on_yield() symbol.

It is defined as a stub in core_test_utils and checks being inside
of GC in libbox.

Somehow it managed to link all this time just fine. And moreover
the linker selected the correct symbol - the one from
core_test_utils.

But while making another patch (not submitted yet), some other
unit test was changed a bit and the watcher unit test link stage
started failing with 'cord_on_yield()' duplicate symbol.

The patch drops core_test_utils from the test and makes it work
with libbox correctly. To support that the test now needs to
initialize the global Lua state.

Actualize changelog based on GitHub release pages changelogs. Some
entries were skipped since they are not relevant to modern packages.
Versions 1.8.1 and 2.0.4 changelogs were merged to 2.1.1 changelog.

Closes #6397

Actualize changelog based on GitHub release pages changelogs. Some
entries were skipped since they are not relevant to modern packages.
Versions 1.8.1 and 2.0.4 changelogs were merged to 2.1.1 changelog.

Part of #6397

This patch extends the 'integration.yml' workflow and adds a new
workflow call for running tests to verify integration between tarantool
and the expiration module.

Part of #5265
Part of #6056
Closes #6528

This commit fixes the following failure:

```
[028] --- wal_off/snapshot_stress.result	Fri Jun  5 06:49:36 2020
[028] +++ wal_off/snapshot_stress.reject	Fri Oct 16 13:48:23 2020
[028] @@ -375,7 +375,7 @@
[028]  ...
[028]  snaps_find_status;
[028]  ---
[028] -- snaps found
[028] +- where are my snapshots?
[028]  ...
[028]  snapshot_check_failed = false
[028]  while #snaps > initial_snap_count do
[028]
```

It happens, because the fiber making snapshots is started after worker
fibers and it works until all worker fibers are done so it might occur
that it doesn't make any snapshots. Fix this by replacing the while-loop
with a repeat-loop, thus ensuring that the worker fiber makes at least
one snapshot.

Closes #5431

Just need to replace scoped guards with labels and add struct keyword to
the sockaddr types.

While we are at it, replace malloc with xmalloc in coio_fill_addrinfo -
we don't check if the returned valued is NULL anyway.

There are just a few places outside coio.cc and coio_buf.h where these
functions are used directly (most users use helpers from coio_buf.h or
xrow_io.h): popen, console, applier.

This is a step towards conversion of coio to C.

This commit makes coio_stat_stat_timeout, coio_waitpid, and
coio_service_start exception-free. None of the functions is used
anywhere in the code except for tests.

This is a step towards conversion of coio to C.

Note, the only place where coio_connect is used is applier_connect,
while coio_accept isn't used anywhere.

This is needed to convert the net.box state machine to C.

So that users that don't have an uri at hand can use it.

This is needed to convert the net.box state machine to C.

Closes #3174

@TarantoolBot document
Title: Field type ANY in SQL

Properties of type ANY in SQL:
1) typeof() with an argument of type ANY returns "any";
2) any value of any type can be implicitly and explicitly cast to the ANY type;
3) a value of type ANY cannot be implicitly cast to any other type;
4) a value of type ANY cannot participate in arithmetic, bitwise, comparison,
   and concationation operations.

After this patch, the built-in SQL function implementation definitions
will use field_type_MAX to indicate that they accept values of any type,
instead of FIELD_TYPE_ANY.

Part of #3174

Prior to this patch, in some cases a struct Expr value with an opcode
TK_INTEGER could have field type ANY. This patch sets such values to the
INTEGER field type.

Part of #3174

This patch extends the 'integration.yml' workflow and adds a new
workflow call for running tests to verify integration between tarantool
and the tarantool-php/queue connector.

Part of #5265
Part of #6056
Closes #6595

This patch forces SQL built-in function implementations to accept
'const struct Mem *' instead of just 'struct Mem *'.

Needed for #4145

This patch removes the MEM_Term flag, because after changes in the SQL
built-in functions, this flag is no longer used.

Needed for #4145

This patch removes the MEM_Dyn flag, because after changes in the SQL
built-in functions, this flag is no longer used.

Needed for #4145

Some of the code is no longer used after changes in the SQL built-in
functions. This patch removes part of the unused code.

Needed for #4145

Part of #4145

Part of #4145

Part of #4145

Part of #4145

This patch refactors UUID() function. Also, UUID(NULL) now returns NULL.

Part of #4145

Part of #4145

Part of #4145

Part of #4145

Part of #4145

This patch refactors RANDOMBLOB() function. Also, RANDOMBLOB(0) now
returns empty string.

part of #4145