test: xlog/checkpoint_daemon.test.lua flaky fails

[avtikhon]

Tarantool version:
Tarantool 2.5.0-12-gba206b484a

OS version:
Linux
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 -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-cast-function-type -Werror

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/746980477#L3792
results file checksum: 7c9571a53f3025f02ab23703939a02d6

https://gitlab.com/tarantool/tarantool/-/jobs/531723107

[164] --- xlog/checkpoint_daemon.result Thu Apr 30 11:50:16 2020
[164] +++ xlog/checkpoint_daemon.reject Thu Apr 30 12:23:22 2020
[164] @@ -105,6 +105,7 @@
[164]  -- third xlog
[164]  for i = 1, row_count_per_wal + 10 do space:insert { no } no = no + 1 end
[164]  ---
[164] +- error: Failed to write to disk
[164]  ...
[190] xlog/checkpoint_daemon.test.lua                                 [ pass ]
[164]  -- fourth xlog
[164]  for i = 1, row_count_per_wal + 10 do space:insert { no } no = no + 1 end
[164]

Steps to reproduce:
on dev1 test host run

l=0 ; while ./test-run.py -j200 `for r in {1..200} ; do echo xlog/checkpoint_daemon.test.lua ; done 2>/dev/null` ; do l=$(($l+1)) ; echo ======== $l ============= ; done

Optional (but very desirable):

• coredump
• backtrace
• netstat