A stomp messaging plugin.
    
    Summary: This adds a new messaging plugin to publish over STOMP.
    
    Test Plan: Unfortunately, you have to set up a broker to really functionally test this.  :(
    
    Reviewers: jskladan, tflink, #resultsdb
    
    Reviewed By: jskladan, #resultsdb
    
    Subscribers: kparal
    
    Differential Revision: https://phab.qa.fedoraproject.org/D1191