Add fedmsg support.
    
    This publishes to fedmsg, if configured.
    
    An important limitation here is that since we currently have only on
    `TestConfiguration` for the project, it is not possible (or I don't see
    a way) to have the test suite run *both* the rhmsg tests *and* the
    fedmsg tests.  You can change the configuration for the tests and run
    one, or the other.