'pause' action may fail with "these ports which should be closed, but are open: 4990, 35347"

[Aurelien Lourot]

May be related to lp:1599636

Seen once on OSCI, but most likely very rare:
https://openstack-ci-reports.ubuntu.com/artifacts/test_charm_pipeline_func_full/openstack/charm-keystone/761561/2/7468/consoleText.test_charm_func_full_10536.txt

FAIL: test_key_distribution_and_rotation (zaza.openstack.charm_tests.keystone.tests.CharmOperationTest)
Verify key rotation.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/tmp.HyL0c87EJd/func/lib/python3.5/site-packages/zaza/openstack/charm_tests/keystone/tests.py", line 84, in test_key_distribution_and_rotation
    with self.pause_resume(['apache2']):
  File "/usr/lib/python3.5/contextlib.py", line 59, in __enter__
    return next(self.gen)
  File "/tmp/tmp.HyL0c87EJd/func/lib/python3.5/site-packages/zaza/openstack/charm_tests/test_utils.py", line 480, in pause_resume
    model_name=self.model_name))
  File "/tmp/tmp.HyL0c87EJd/func/lib/python3.5/site-packages/zaza/openstack/utilities/generic.py", line 53, in assertActionRanOK
    raise AssertionError(msg)
AssertionError: Action 'pause' exited with status 'failed': 'Couldn't pause: Services should be paused but these ports which should be closed, but are open: 4990, 35347, Unit paused.'