Add supporting of xfail_strict ini parameter

[gdyuldin]

Py.test's with xfail_strict=true treat XPASS result as an failed. This patch adds same behaviour for jira marked tests.

[codecov-io]

Codecov Report

Merging #90 into master will increase coverage by 0.05%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   97.91%   97.96%   +0.05%     
==========================================
  Files           1        1              
  Lines         192      197       +5     
==========================================
+ Hits          188      193       +5     
  Misses          4        4

Impacted Files	Coverage Δ
pytest_jira.py	97.96% <100%> (+0.05%)	:arrow_up:

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[gdyuldin]

Is information about xfail_strict in the README will be enough?

[lukas-bednar]

Could you please update also Usage section, there is example of all options in jira.cfg.

[gdyuldin]

xfail_strict should be on the pytest ini file (first of pytest.ini | tox.ini | setup.cfg), not on jira.cfg.

[lukas-bednar]

Oh, I didn't get this .. then all is OK !

[lukas-bednar]

Thank you!