Start the HTTP change monitoring thread.

def start(self):
        """
        Start the HTTP change monitoring thread.

        """
        # Store reference to message queue in module global variable, so that
        # our Bottle app handler functions have easy access to it.
        global _Q_ROUTE_SPEC
        _Q_ROUTE_SPEC = self.q_route_spec

        logging.info("Http watcher plugin: "
                     "Starting to watch for route spec on "
                     "'%s:%s/route_spec'..." %
                     (self.conf['addr'], self.conf['port']))