test: flaky box/select.test.lua test

[avtikhon]

Tarantool version:
Tarantool 2.7.0-43-gf058b8acd
Target: Darwin-x86_64-RelWithDebInfo
Build options: cmake . -DCMAKE_INSTALL_PREFIX=/usr/local -DENABLE_BACKTRACE=ON
Compiler: /Library/Developer/CommandLineTools/usr/bin/cc /Library/Developer/CommandLineTools/usr/bin/c++
C_FLAGS: -Wno-unknown-pragmas -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -msse2 -std=c11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-gnu-alignof-expression -Werror
CXX_FLAGS: -Wno-unknown-pragmas -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -msse2 -std=c++11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-invalid-offsetof -Wno-gnu-alignof-expression -Werror

OS version:
OSX 15

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/846994549#L4861

artifacts.zip

results file checksum: 7a48e9ad1c4981a3bceebb0e71586376

[041] --- box/select.result	Sat Aug 22 05:06:33 2020
[041] +++ /tmp/tnt/rejects/box/select.reject	Fri Nov 13 05:29:43 2020
[041] @@ -354,6 +354,27 @@
[041]  ...
[041]  test.select(s.index[0], 1)
[041]  ---
[041] +- different result from select_ffi and select_luac
[041] +- - [1, 1, 2, 3]
[041] +  - [2, 1, 2, 3]
[041] +  - [3, 1, 2, 3]
[041] +  - [4, 1, 2, 3]
[041] +  - [5, 1, 2, 3]
[041] +  - [6, 1, 2, 3]
[041] +  - [7, 1, 2, 3]
[041] +  - [8, 1, 2, 3]
[041] +  - [9, 1, 2, 3]
[041] +  - [10, 1, 2, 3]
[041] +  - [11, 1, 2, 3]
[041] +  - [12, 1, 2, 3]
[041] +  - [13, 1, 2, 3]
[041] +  - [14, 1, 2, 3]
[041] +  - [15, 1, 2, 3]
[041] +  - [16, 1, 2, 3]
[041] +  - [17, 1, 2, 3]
[041] +  - [18, 1, 2, 3]
[041] +  - [19, 1, 2, 3]
[041] +  - [20, 1, 2, 3]
[041]  - - [1, 1, 2, 3]
[041]  ...
[041]  test.select(s.index[0], {1})

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat