test: flaky connect issues on swim/swim.test.lua test

[avtikhon]

Tarantool version:
Tarantool 2.6.0-142-g72fc325fc
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 -m64 -fmessage-length=0 -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -DNDEBUG -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 -m64 -fmessage-length=0 -D_FORTIFY_SOURCE=2 -fstack-protector -funwind-tables -fasynchronous-unwind-tables -DNDEBUG -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:

1. openSUSE 15.1
2. Debian 10

Bug description:

1. https://gitlab.com/tarantool/tarantool/-/jobs/771802091#L1946

artifacts.zip

results file checksum: 9f1423cf502adfd16611dd5e839b57e4

[008] --- swim/swim.result	Sun Oct  4 17:51:33 2020
[008] +++ swim/swim.reject	Sun Oct  4 17:55:02 2020
[008] @@ -1500,7 +1500,6 @@
[008]    is_new_generation: true
[008]    is_update: true
[008]    is_new_payload: true
[008] -  is_new_uri: true
[008]    is_new_incarnation: true
[008]  ...
[008]  -- Generation is static parameter.
[008] 

2. https://gitlab.com/tarantool/tarantool/-/jobs/822794741#L4903

artifacts.zip

results file checksum: a127e3c07b933d5e6602cb14e0f6e728

[436] --- swim/swim.result	Fri Oct 30 20:38:03 2020
[436] +++ var/rejects/swim/swim.reject	Sat Oct 31 12:39:56 2020
[436] @@ -306,7 +306,7 @@
[436]  old_self
[436]  ---
[436]  - uri: 127.0.0.1:<port>
[436] -  status: left
[436] +  status: alive
[436]    incarnation: cdata {generation = 0ULL, version = 1ULL}
[436]    uuid: 00000000-0000-1000-8000-000000000001
[436]    payload_size: 0
[436] 

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat