test: flaky replication-py/multi.test.py test

[avtikhon]

Tarantool version:
Tarantool 2.6.0-114-g0670099a7c
Target: Linux-x86_64-RelWithDebInfo
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:
Linux (Debian 9)

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/759595110#L4134

artifacts.zip

results file checksum: 0ee35fafd167b81134a40347173af91a

[025] --- replication-py/multi.result	Fri Jun  5 06:51:39 2020
[025] +++ replication-py/multi.reject	Sun Sep 27 16:08:32 2020
[025] @@ -30,9 +30,12 @@
[025]  Create a test space
[025]  _ = box.schema.space.create('test')
[025]  ---
[025] +- error: Can't modify data because this instance is in read-only mode.
[025]  ...
[025]  _ = box.space.test:create_index('primary')
[025]  ---
[025] +- error: '[string "_ = box.space.test:create_index(''primary'')"]:1: attempt to index
[025] +    field ''test'' (a nil value)'
[025]  ...
[025]  server 1 is ok
[025]  server 2 is ok
[025] @@ -48,9 +51,9 @@
[025]  done
[025]  
[025]  Check data
[025] -server 1 is ok
[025] -server 2 is ok
[025] -server 3 is ok
[025] +server 1 is not ok
[025] +server 2 is not ok
[025] +server 3 is not ok
[025]  Done
[025]  
[025]  
[025] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat