openqa/dispatcher: first cut at supporting fedora-messaging
    
    This is a big change to support fedora-messaging based consumers
    instead of fedmsg ones in the openqa/dispatcher role. This needs
    the fedora-messaging branch of fedora_openqa, until that is
    merged to stable. For now this is all conditionalized so prod
    will continue to use fedmsg. This also improves some variable
    usage and documentation in the fedmsg path too.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>