Zuul occassionally fails to complete event actions

[ConsoleCatzirl]

Temporary dns failures for api.github.com occasionally cause zuul to fail to complete actions such as setting status, and the following traceback can be seen in the server.log:

 2017-01-19 21:03:08,677 ERROR zuul.Scheduler: Exception in run handler:
 Traceback (most recent call last):
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/zuul/scheduler.py", line 1019, in run
     self.process_event_queue()
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/zuul/scheduler.py", line 1066, in process_event_queue
     change = pipeline.source.getChange(event, project)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/zuul/source/github.py", line 61, in getChange
     change.files = self.getPullFiles(project, change.number)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/zuul/source/github.py", line 92, in getPullFiles
     return self.connection.getPullFileNames(owner, project, number)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/zuul/connection/github.py", line 306, in getPullFileNames
     integration_key_file = config.get('integration_key')
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/github3/github.py", line 930, in pull_request
     json = self._json(self._get(url), 200)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/github3/models.py", line 187, in _get
     return self.session.get(url, **kwargs)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/requests/sessions.py", line 501, in get
     return self.request('GET', url, **kwargs)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/github3/session.py", line 88, in request
     response = super(GitHubSession, self).request(*args, **kwargs)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/requests/sessions.py", line 488, in request
     resp = self.send(prep, **send_kwargs)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/requests/sessions.py", line 609, in send
     r = adapter.send(request, **kwargs)
   File "/opt/venvs/zuul/local/lib/python2.7/site-packages/requests/adapters.py", line 487, in send
     raise ConnectionError(e, request=request)
 ConnectionError: HTTPSConnectionPool(host='api.github.com', port=443): Max retries exceeded with url: /repos/BonnyCI/hoist/pulls/61 (Caused by NewConnectionError('<requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7f35c05937d0>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution',))