Default play names to the hosts the play was run against

Fixes #1030

awx/plugins/callback/job_event_callback.py

@@ -463,6 +463,10 @@ class JobCallbackModule(BaseCallbackModule):
 
     def v2_playbook_on_play_start(self, play):
         setattr(self, 'play', play)
+        # Ansible 2.0.0.2 doesn't default .name to hosts like it did in 1.9.4,
+        # though that default will likely return in a future version of Ansible.
+        if not hasattr(play, 'name') or play.name == '':
+            play.name = ', '.join(play.hosts)
         self._log_event('playbook_on_play_start', name=play.name,
                         pattern=play.hosts)