Fix functional tests in the test suite.
    
    Summary:
    The issue is that the messaging plugins are defined as setuptools
    entry-points, and those live in the .egg-info directory.  If you're developing
    locally, that directory is usually present in `pwd` due to `python setup.py
    develop` or `python setup.py egg-info`.  But in the spec file, we install to a
    directory that is not in the PYTHONPATH.  This change re-enables the `-F`
    option but also specifies the PYTHONPATH so that the entry-points are found and
    the tests pass.
    
    This should fix T874.
    
    Test Plan: Try building the rpm in mock.  It works!
    
    Reviewers: tflink, jskladan, mkrizek
    
    Reviewed By: mkrizek
    
    Maniphest Tasks: T874
    
    Differential Revision: https://phab.qa.fedoraproject.org/D1073