test: flaky box/schema_reload.test.lua test

[avtikhon]

Tarantool version:
Tarantool 2.7.0-43-gf058b8acd
Target: Linux-x86_64-Debug
Build options: cmake . -DCMAKE_INSTALL_PREFIX=/usr/local -DENABLE_BACKTRACE=ON
Compiler: /usr/bin/cc /usr/bin/c++
C_FLAGS: -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -fopenmp -msse2 -std=c11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-format-truncation -Wno-gnu-alignof-expression -fno-gnu89-inline -Wno-cast-function-type -Werror
CXX_FLAGS: -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -fopenmp -msse2 -std=c++11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-format-truncation -Wno-invalid-offsetof -Wno-gnu-alignof-expression -Wno-cast-function-type -Werror

OS version:
CentOS 7

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/847213709#L4378

results file checksum: e07fa0f0d38ad1619c6206b30f8c8e8f

[115] --- box/schema_reload.result	Fri Nov 13 06:46:13 2020
[115] +++ /rw_bins/test/var/rejects/box/schema_reload.reject	Fri Nov 13 06:49:06 2020
[115] @@ -111,7 +111,7 @@
[115]  ...
[115]  requests < reloads
[115]  ---
[115] -- true
[115] +- false
[115]  ...
[115]  -- cleanup
[115]  request_fiber:cancel()
[115] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat