Bump required pytest version

[MartinBasti]

Fixes internal error cause by flexmock:

INTERNALERROR>   File "/usr/lib/python2.7/site-packages/flexmock.py", line 1249, in call_runtest_hook
1129
INTERNALERROR>     teardown.duration = ret.duration
INTERNALERROR> AttributeError: 'CallInfo' object has no attribute 'duration'

flexmock 0.10.5 requires newer pytest, but doesn't properly specifies min requirements

Signed-off-by: Martin Basti mbasti@redhat.com

Maintainers will complete the following section

• [ ] Commit messages are descriptive enough
• [ ] Code coverage from testing does not decrease and new code is covered
• [ ] JSON/YAML configuration changes are updated in the relevant schema
• [ ] Pull request has a link to an osbs-docs PR for user documentation updates

[MartinBasti]

nope, 4.6.11 is the latest py2 supported version. Closing