Pytest replaces nosetests
    
    Nosetests tool is deprecated. Also tools supporting Python2.6
    test-environment are deprecated one by one. So this was removed too.
    Pytest tool will run the unit tests. When 'make test' is run, all
    neccessary dependencies are installed by pip.
    
    Fixes: #501
    JIRA: RHELCMP-578
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>