[CI] smoke tests failed due to keystone being restarted during test

[Alex Kavanagh]

Probably need to implement timed retries for openstack services during tests as this is non HA and we should expect failures to occur on services due to async nature of underlying system:

e.g.

2021-02-18 02:33:14 [INFO] Creating domain, project and user for Kerberos tests.
2021-02-18 02:33:18 [ERROR] {'default_alias': 'zaza-4051568f6b30'}
2021-02-18 02:33:18 [ERROR] Model default_alias (zaza-4051568f6b30)
Traceback (most recent call last):
  File "/tmp/tmp.qZREbSPSUx/func-smoke/lib/python3.5/site-packages/urllib3/connectionpool.py", line 706, in urlopen
    chunked=chunked,
  File "/tmp/tmp.qZREbSPSUx/func-smoke/lib/python3.5/site-packages/urllib3/connectionpool.py", line 445, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/tmp/tmp.qZREbSPSUx/func-smoke/lib/python3.5/site-packages/urllib3/connectionpool.py", line 440, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/lib/python3.5/http/client.py", line 1242, in getresponse
    response.begin()
  File "/usr/lib/python3.5/http/client.py", line 311, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python3.5/http/client.py", line 280, in _read_status
    raise RemoteDisconnected("Remote end closed connection without"
http.client.RemoteDisconnected: Remote end closed connection without response

...

  File "/tmp/tmp.qZREbSPSUx/func-smoke/lib/python3.5/site-packages/zaza/openstack/charm_tests/kerberos/setup.py", line 135, in openstack_setup_kerberos
    enabled=True)

...

  File "/tmp/tmp.qZREbSPSUx/func-smoke/lib/python3.5/site-packages/keystoneauth1/session.py", line 1028, in _send_request
    raise exceptions.ConnectFailure(msg)
keystoneauth1.exceptions.connection.ConnectFailure: Unable to establish connection to http://172.17.115.5:5000/v3/auth/tokens: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response',))

[Corey Bryant (corey.bryant)]

Looking through some recent gate runs for this charm and it doesn't appear the failures are very frequent so I'm going to triage this as low.