Add configs for stg.
    
    This treats the fedora infrastructure staging environment just like
    another secondary architecture (at dgilmore's suggestion in
    the fedora-releng channel today).
    
    Fixed after initial review on the buildsys list[0].
    https://lists.fedoraproject.org/pipermail/buildsys/2015-April/004629.html
    
    Signed-off-by: Ralph Bean <rbean@redhat.com>