MetadataNamespacesTest.test_basic_metadata_definition_namespaces intermittently fails in the gate with "Could not find namespace tempest-test-ns-"

[Matt Riedemann]

Seen here:

http://logs.openstack.org/60/600260/1/gate/nova-cells-v1/0735337/job-output.txt.gz#_2018-09-08_22_39_02_292222

2018-09-08 22:39:02.292222 | primary | Captured traceback:
2018-09-08 22:39:02.292315 | primary | ~~~~~~~~~~~~~~~~~~~
2018-09-08 22:39:02.292466 | primary | Traceback (most recent call last):
2018-09-08 22:39:02.292758 | primary | File "tempest/api/image/v2/test_images_metadefs_namespaces.py", line 44, in test_basic_metadata_definition_namespaces
2018-09-08 22:39:02.292991 | primary | bodys = self.namespaces_client.list_namespaces()['namespaces']
2018-09-08 22:39:02.293223 | primary | File "tempest/lib/services/image/v2/namespaces_client.py", line 45, in list_namespaces
2018-09-08 22:39:02.293345 | primary | resp, body = self.get(url)
2018-09-08 22:39:02.293517 | primary | File "tempest/lib/common/rest_client.py", line 294, in get
2018-09-08 22:39:02.293683 | primary | return self.request('GET', url, extra_headers, headers)
2018-09-08 22:39:02.293855 | primary | File "tempest/lib/common/rest_client.py", line 675, in request
2018-09-08 22:39:02.293995 | primary | self._error_checker(resp, resp_body)
2018-09-08 22:39:02.294178 | primary | File "tempest/lib/common/rest_client.py", line 781, in _error_checker
2018-09-08 22:39:02.294613 | primary | raise exceptions.NotFound(resp_body, resp=resp)
2018-09-08 22:39:02.294799 | primary | tempest.lib.exceptions.NotFound: Object not found
2018-09-08 22:39:02.295224 | primary | Details: {u'title': u'Not Found', u'code': u'404 Not Found', u'message': u'Could not find namespace tempest-test-ns-1299063839<br /><br />\n\n\n'}

http://logstash.openstack.org/#dashboard/file/logstash.json?query=message%3A%5C%22Could%20not%20find%20namespace%20tempest-test-ns%5C%22%20AND%20tags%3A%5C%22console%5C%22&from=7d

17 hits in 7 days, check and gate, all failures, master and stable/rocky.