Flaky cron test

[Andreas Hasenack]

23:48:37 Failure in test test_process_alerts_cron (basic.test_service.CronTest)
23:48:37 Traceback (most recent call last):
23:48:37 File "/usr/lib/python3.4/unittest/case.py", line 57, in testPartExecutor
23:48:37 yield
23:48:37 File "/usr/lib/python3.4/unittest/case.py", line 574, in run
23:48:37 testMethod()
23:48:37 File "/var/jenkins/workspace/charm-integration-test/tests/basic/test_service.py", line 201, in test_process_alerts_cron
23:48:37 self.assertEqual(output, "")
23:48:37 File "/usr/lib/python3.4/unittest/case.py", line 794, in assertEqual
23:48:37 assertion_func(first, second, msg=msg)
23:48:37 File "/usr/lib/python3.4/unittest/case.py", line 1167, in assertMultiLineEqual
23:48:37 self.fail(self._formatMessage(msg, standardMsg))
23:48:37 File "/usr/lib/python3.4/unittest/case.py", line 639, in fail
23:48:37 raise self.failureException(msg)
23:48:37 AssertionError: "Warning: Permanently added '10.0.3.54' ([110 chars]de 1" != ''
23:48:37 - Warning: Permanently added '10.0.3.54' (ECDSA) to the list of known hosts.
23:48:37 - Connection to 10.0.3.54 closed.
23:48:37 - ERROR subprocess encountered error code 1

I believe the test should ignore the ssh warnings. Note that the user running these tests has this ssh config:
Host 10.0.3.*
    UserKnownHostsFile /dev/null
    StrictHostKeyChecking no