Ansible launcher: use correct ZMQ port

We use 8888.  Where did 8881 even come from?
(This should probably be configurable.)

Change-Id: I94311fc0ba63b9c29a9e7bc92574ef3a63750c95

zuul/launcher/ansiblelaunchserver.py

@@ -145,7 +145,7 @@ class LaunchServer(object):
         # Setup ZMQ
         self.zcontext = zmq.Context()
         self.zsocket = self.zcontext.socket(zmq.PUB)
-        self.zsocket.bind("tcp://*:8881")
+        self.zsocket.bind("tcp://*:8888")
 
         # Setup Gearman
         server = self.config.get('gearman', 'server')