test: flaky box/net.box_discard_gh-3107.test.lua test

[avtikhon]

Tarantool version:
| Tarantool 2.7.0-75-gfe1efabb6
| 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

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/874398764#L4693

artifacts.zip

results file checksum: 314f85aa0efa27c15446910c950d68c9

[025] box/net.box_discard_gh-3107.test.lua                            [ fail ]
[025] 
[025] Test failed! Result content mismatch:
[025] --- box/net.box_discard_gh-3107.result	Wed Nov 25 15:57:37 2020
[025] +++ /tmp/tnt/rejects/box/net.box_discard_gh-3107.reject	Thu Nov 26 15:58:17 2020
[025] @@ -27,22 +27,23 @@
[025]  ...
[025]  pk = s:create_index('pk')
[025]  ---
[025] +- error: Space '#557' does not exist
[025]  ...
[025]  s:replace{1}
[025]  ---
[025] -- [1]
[025] +- error: 'No index #0 is defined in space ''test'''
[025]  ...
[025]  s:replace{2}
[025]  ---
[025] -- [2]
[025] +- error: 'No index #0 is defined in space ''test'''
[025]  ...
[025]  s:replace{3}
[025]  ---
[025] -- [3]
[025] +- error: 'No index #0 is defined in space ''test'''
[025]  ...
[025]  s:replace{4}
[025]  ---
[025] -- [4]
[025] +- error: 'No index #0 is defined in space ''test'''
[025]  ...
[025]  c = net:connect(box.cfg.listen)
[025]  ---
[025] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat