Description of problem:
The EPEL package python2-requests-mock-1.5.0 includes a pytest plugin that is incompatible with the version of pytest shipped in base/7 repo (pytest-2.7.0).

Trying to run `py.test` with any arguments will cause the program to exit with an assertion failure when both packages are installed.

Version-Release number of selected component (if applicable):
python2-requests-mock 1.5.0-1.el7 (from EPEL-7)
pytest 2.7.0-1.el7 (from base/7)

How reproducible:
Issue can be reproduced consistently.

Steps to Reproduce:
1. yum install -y pytest python2-requests-mock
2. py.test --help 

Actual results:
py.test will fail to start and print a stack trace:

Traceback (most recent call last):
  File "/usr/bin/py.test", line 9, in <module>
    load_entry_point('pytest==2.7.0', 'console_scripts', 'py.test-2.7')()
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 32, in main
    config = _prepareconfig(args, plugins)
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 85, in _prepareconfig
    pluginmanager=pluginmanager, args=args)
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 521, in __call__
    return self._docall(self.methods, kwargs)
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 528, in _docall
    firstresult=self.firstresult).execute()
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 393, in execute
    return wrapped_call(method(*args), self.execute)
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 109, in wrapped_call
    wrap_controller.send(call_outcome)
  File "/usr/lib/python2.7/site-packages/_pytest/helpconfig.py", line 28, in pytest_cmdline_parse
    config = outcome.get_result()
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 138, in get_result
    py.builtin._reraise(*ex)
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 123, in __init__
    self.result = func()
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 394, in execute
    res = method(*args)
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 636, in pytest_cmdline_parse
    self.parse(args)
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 746, in parse
    self._preparse(args)
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 713, in _preparse
    self.pluginmanager.consider_setuptools_entrypoints()
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 282, in consider_setuptools_entrypoints
    self.register(plugin, name=name)
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 189, in register
    reg(plugin, name)  # may call addhooks
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 611, in _register_plugin
    call_plugin(plugin, "pytest_addoption", {'parser': self._parser})
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 360, in call_plugin
    kwargs=kwargs, firstresult=True).execute()
  File "/usr/lib/python2.7/site-packages/_pytest/core.py", line 394, in execute
    res = method(*args)
  File "/usr/lib/python2.7/site-packages/requests_mock/contrib/_pytest_plugin.py", line 9, in pytest_addoption
    default=False)
  File "/usr/lib/python2.7/site-packages/_pytest/config.py", line 212, in addini
    assert type in (None, "pathlist", "args", "linelist")
AssertionError

Expected results:
py.test should print the normal help message.


Additional info:
The plugin in python2-requests-mock _appears_ to be compatible with pytest versions starting from 2.9.0; I have only tested that `pytest --help` can be successfully run again.

This was tested with upstream versions of the packages in PyPi using python-virtualenv and python2-pip. The following works:

$ virtualenv env; source env/bin/activate;
$ pip install pytest==2.9.0 requests-mock==1.5.0;
$ env/bin/py.test --help; # This works!

but this doesn't work

$ virtualenv env; source env/bin/activate;
$ pip install pytest==2.8.7 requests-mock==1.5.0;
$ env/bin/py.test --help; # This does NOT work!

The upstream source for requests-mock in GitHub does not define a version requirement for pytest. The relevant commit is here:
https://github.com/jamielennox/requests-mock/commit/a455a735d7edba5d064380eb054021a11d076f57