Simplify and modernize setup.py, drop setup.py test support
    
    This drops the `python setup.py test` support (which is more or
    less considered unnecessary and useless these days), and also
    the --nodeps stuff, which we shouldn't need now we're much more
    heavily Python 3-only (and don't use fedmsg any more).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>