test: flaky box/misc.test.lua test

[avtikhon]

Tarantool version:
Tarantool 2.5.0-28-ga739c94892
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 -fprofile-arcs -ftest-coverage -std=c11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-format-truncation -fno-gnu89-inline -Wno-cast-function-type -Werror
CXX_FLAGS: -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -fopenmp -msse2 -fprofile-arcs -ftest-coverage -std=c++11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Wno-format-truncation -Wno-invalid-offsetof -Wno-cast-function-type -Werror

OS version:
Linux

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/553852595

 [069] --- box/misc.result	Thu May 14 16:08:44 2020
 [069] +++ box/misc.reject	Fri May 15 08:05:24 2020
 [069] @@ -964,11 +964,11 @@
 [069]  ...
 [069]  rows == expected_rows
 [069]  ---
 [069] -- true
 [069] +- false
 [069]  ...
 [069]  lsn == expected_lsn
 [069]  ---
 [069] -- true
 [069] +- false
 [069]  ...
 [069]  box.cfg{too_long_threshold = too_long_threshold}
 [069]  ---

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat