test: flaky box/net.box_incorrect_iterator_gh-841.test.lua

[avtikhon]

Tarantool version:
Tarantool 2.6.0-153-gc8dda037e
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/785099690#L3850

artifacts.zip

results file checksum: 3c2b74ee82a7689f29f8a8e50d804ecb

[009] --- box/net.box_incorrect_iterator_gh-841.result	Mon Oct 12 08:56:13 2020
[009] +++ box/net.box_incorrect_iterator_gh-841.reject	Mon Oct 12 10:19:41 2020
[009] @@ -475,6 +475,7 @@
[009]  ...
[009]  box.schema.user.revoke('guest', 'execute', 'universe')
[009]  ---
[009] +- error: Invalid key part count in an exact match (expected 1, got 0)
[009]  ...
[009]  cn:close()
[009]  ---
[009] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat