Include the gstreamer plugin in gstreamer1-plugin-openh264 subpackage
    
    Sadly, the current build infrastructure doesn't let us build any
    external packages against openh264, so we have to include the gstreamer
    plugin build in the same source rpm.
    
    https://fedorahosted.org/fesco/ticket/1496 includes some background info
    why it can't be a separate package.