After adding the autorequiring luatest [1,2], there is no need to use
the following approach now:

```
local t = require('luatest')
local g = t.group()

server:exec(function()
    local t = require('luatest') -- duplicate
    t.assert(...)
end)
```

Modern approach looks like:

```
local t = require('luatest')
local g = t.group()

-- `t` already available in the remote server
server:exec(function() t.assert(...) end)

-- also it works with any variable
local my_custom_t = require('luatest')

server:exec(function()
    my_custom_t.assert(...) -- already available
end)
```

[1] tarantool/luatest#277
[2] tarantool/luatest#289

Part of tarantool/luatest#233

NO_DOC=test fix
NO_TEST=test fix
NO_CHANGELOG=test fix

Some internal modules have been recently copied to luatest repo [1,2]
and now they can be safely removed, and the corresponding functionality
from luatest can be used instead.

Affected modules:

- test/luatest_helpers/server.lua

[1] tarantool/luatest#258
[2] tarantool/luatest#266

Closes tarantool/luatest#239

NO_DOC=testing stuff
NO_TEST=testing stuff
NO_CHANGELOG=testing stuff

Currently, we include the bad field number into the error message
manually, using tt_sprintf, which looks cumbersome. For some fields,
we don't include it at all (e.g. invalid constraint definition).
Let's include it into the error message format instead.

Part of #7933

NO_DOC=verbosity
NO_CHANGELOG=later

Some internal modules have been recently copied to luatest repo [1,2,3]
and now they can be safely removed, and the corresponding functionality
from luatest can be used instead.

Affected modules:

- test/luatest_helpers/misc.lua
- test/luatest_helpers/fiber.lua
- test/luatest_helpers/proxy/*

[1] https://github.com/tarantool/luatest/pull/247
[2] https://github.com/tarantool/luatest/pull/248
[3] https://github.com/tarantool/luatest/pull/255

Closes tarantool/luatest#238
Closes tarantool/luatest#251

NO_DOC=testing stuff
NO_TEST=testing stuff
NO_CHANGELOG=testing stuff

The helper skips a running test with luatest.skip_if in case executed by
Tarantool Enterprise. It's better than checking the package directly in
the test, because luatest.skip_if prints the reason why the test is
skipped.

NO_DOC=test
NO_CHANGELOG=test

This is needed to factor out the function that decodes space format so
that it can be used for online space upgrade. It's not a big deal,
because we already use ER_WRONG_SPACE_OPTIONS if space options specified
on space creation/alter are wrong so using ER_WRONG_SPACE_FORMAT would
only be consistent.

NO_DOC=minor change in error message
NO_CHANGELOG=minor change in error message

Implement ability to set compression for tuple fields. Compression type
for tuple fields is set in the space format, and can be set during space
creation or during setting of a new space format.
```lua
format = {{name = 'x', type = 'unsigned', compression = 'none'}}
space = box.schema.space.create('memtx_space', {format = format})
space:drop()
space = box.schema.space.create('memtx_space')
space:format(format)
```
For opensource build only one compression type ('none') is
supported. This type of compression means its absence, so
it doesn't affect something.

Part of #2695

NO_CHANGELOG=stubs for enterprise version
NO_DOC=stubs for enterprise version