PROTON-1800: issue not completely fixed, ignore the failing test

[jiridanek]

@astitcher this implements the decorator you suggested to skip test if AssertionErrors occurred.

[astitcher]

I think the name of the new decorator is too general. How about something like "skipOnFailure" or perhaps "ignoreFailure"?

[codecov-commenter]

Codecov Report

Merging #253 into master will increase coverage by 0.00%.
The diff coverage is 81.81%.

@@           Coverage Diff           @@
##           master     #253   +/-   ##
=======================================
  Coverage   83.09%   83.09%           
=======================================
  Files         339      339           
  Lines       41362    41368    +6     
=======================================
+ Hits        34368    34373    +5     
- Misses       6994     6995    +1     

Impacted Files	Coverage Δ
...on/test_PROTON_1800_syncrequestresponse_fd_leak.py	91.20% <81.81%> (-1.30%)	⬇️
c/src/proactor/epoll.c	81.54% <0.00%> (-0.17%)	⬇️
c/tests/threaderciser.c	83.21% <0.00%> (-0.06%)	⬇️
c/src/core/codec.c	82.61% <0.00%> (+0.24%)	⬆️

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