thttpclient_ssl flaky test on Linux_i386

[timotheecour]

https://dev.azure.com/nim-lang/255dfe86-e590-40bb-a8a2-3c0295ebdeb1/_apis/build/builds/10874/logs/99
tests/misc/trunner_special.nim
https://dev.azure.com/nim-lang/Nim/_build/results?buildId=10874&view=logs&jobId=ba7bbfa4-f55c-5c34-6d52-1b6b4edd3f37&j=ba7bbfa4-f55c-5c34-6d52-1b6b4edd3f37

after nim-lang#16221

2020-12-12T08:08:45.1946709Z �[32mPASS: �[36mtests/misc/trunner.nim c                                    �[34m (18.86 sec)�[0m
2020-12-12T08:08:45.1947529Z �[32mPASS: �[36mtests/misc/trunner.nim cpp                                  �[34m (16.59 sec)�[0m
2020-12-12T08:08:45.1948240Z �[1m�[31mFAIL: �[36mtests/misc/trunner_special.nim c�[0m
2020-12-12T08:08:45.1948919Z �[1m�[36mTest "tests/misc/trunner_special.nim" in category "misc"�[0m
2020-12-12T08:08:45.1949551Z �[1m�[31mFailure: reExitcodesDiffer�[0m
2020-12-12T08:08:45.1950067Z �[33mExpected:�[0m
2020-12-12T08:08:45.1950553Z �[1mexitcode: 0
2020-12-12T08:08:45.1950979Z �[0m
2020-12-12T08:08:45.1951432Z �[33mGotten:�[0m
2020-12-12T08:08:45.1951895Z �[1mexitcode: 1
2020-12-12T08:08:45.1952152Z 
2020-12-12T08:08:45.1952425Z Output:
2020-12-12T08:08:45.1952654Z 
2020-12-12T08:08:45.1953144Z [Suite] SSL certificate check - disabled
2020-12-12T08:08:45.1953433Z 
2020-12-12T08:08:45.1953924Z [Suite] SSL certificate check - httpclient
2020-12-12T08:08:45.1954835Z          no-common-name (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1956590Z          no-subject (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1957540Z          incomplete-chain (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1957928Z 
2020-12-12T08:08:45.1958318Z [Suite] SSL certificate check - httpclient - threaded
2020-12-12T08:08:45.1959068Z          no-common-name (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1959968Z          no-subject (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1960898Z          incomplete-chain (dubious_broken) raised: error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
2020-12-12T08:08:45.1961382Z Traceback (most recent call last)
2020-12-12T08:08:45.1961633Z thttpclient_ssl.nim(173) thttpclient_ssl
2020-12-12T08:08:45.1961887Z threadpool.nim(263)      ^
2020-12-12T08:08:45.1962125Z deepcopy.nim(190)        genericDeepCopy
2020-12-12T08:08:45.1962396Z deepcopy.nim(152)        genericDeepCopyAux
2020-12-12T08:08:45.1962715Z SIGSEGV: Illegal storage access. (Attempt to read from nil?)
2020-12-12T08:08:45.1963377Z Error: execution of an external program failed: '/home/vsts/.cache/nim/thttpclient_ssl_d/thttpclient_ssl '
2020-12-12T08:08:45.1964294Z /home/vsts/work/1/s/tests/misc/trunner_special.nim(22, 12): Check failed: ret == 0
2020-12-12T08:08:45.1964625Z ret was 1
2020-12-12T08:08:45.1964745Z 
2020-12-12T08:08:45.1965034Z �[0m
2020-12-12T08:08:45.1965575Z �[32mPASS: �[36mtests/misc/trunner_special.nim cpp                          �[34m (36.24 sec)�[0m

note that before PR, this wasn't being tested:

matrix:
        os: [ubuntu-18.04, macos-10.15, windows-2019]
        cpu: [amd64]

[timotheecour]

=> nim-lang#16338