intermittent hmac test failure

this happens occasionally in gate and occasionally on my dev machine

======================================================================
FAIL: ceilometer.tests.test_notification.TestRealNotificationHA.test_notification_service_no_secret
tags: worker-2
----------------------------------------------------------------------
Empty attachments:
  stderr
  stdout

Traceback (most recent call last):
  File "/opt/stack/ceilometer/.tox/py-mysql/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched
    return func(*args, **keywargs)
  File "ceilometer/tests/test_notification.py", line 395, in test_notification_service_no_secret
    self.assertFalse(fake_hmac.called)
  File "/opt/stack/ceilometer/.tox/py-mysql/lib/python2.7/site-packages/unittest2/case.py", line 696, in assertFalse
    raise self.failureException(msg)
AssertionError: True is not false