test: flaky box/access_sysview.test.lua test

[avtikhon]

Tarantool version:
Tarantool 2.6.0-93-gace41229f
Target: Linux-x86_64-RelWithDebInfo
Build options: cmake . -DCMAKE_INSTALL_PREFIX=/usr -DENABLE_BACKTRACE=ON
Compiler: /usr/bin/cc /usr/bin/c++
C_FLAGS:-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -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
CXX_FLAGS:-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -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

OS version:
Linux (Fedora 28)

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/746695508#L2671
checksum: d6136f214b81556b1858e05970a90963

[086] --- box/access_sysview.result	Sat Sep 19 11:06:18 2020
[086] +++ box/access_sysview.reject	Sat Sep 19 11:10:53 2020
[086] @@ -258,7 +258,7 @@
[086]  ...
[086]  #box.space._vpriv:select{}
[086]  ---
[086] -- 82
[086] +- 81
[086]  ...
[086]  #box.space._vfunc:select{}
[086]  ---
[086] @@ -290,7 +290,7 @@
[086]  ...
[086]  #box.space._vpriv:select{}
[086]  ---
[086] -- 82
[086] +- 81
[086]  ...
[086]  #box.space._vfunc:select{}
[086]  ---
[086] @@ -552,7 +552,7 @@
[086]  ...
[086]  #box.space._vfunc:select{} == func_cnt
[086]  ---
[086] -- true
[086] +- false
[086]  ...
[086]  box.session.su('admin')
[086]  ---
[086] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat