test_401_enable_qos sometimes fails with 'qos' not found in ovs_agent['configurations']['extensions']

[Aurelien Lourot]

Transient. Seen on hirsute-wallaby:
https://openstack-ci-reports.ubuntu.com/artifacts/8e5/811172/2/check/hirsute-wallaby/8e5a519/job-output.txt
https://review.opendev.org/c/openstack/charm-neutron-gateway/+/811172

FAIL: test_401_enable_qos (zaza.openstack.charm_tests.neutron.tests.NeutronGatewayTest)
Check qos settings set via neutron-api charm.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/zaza/openstack/charm_tests/neutron/tests.py", line 135, in test_401_enable_qos
    self._validate_openvswitch_agent_qos()
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/tenacity/__init__.py", line 324, in wrapped_f
    return self(f, *args, **kw)
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/tenacity/__init__.py", line 404, in __call__
    do = self.iter(retry_state=retry_state)
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/tenacity/__init__.py", line 360, in iter
    raise retry_exc.reraise()
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/tenacity/__init__.py", line 193, in reraise
    raise self.last_attempt.result()
  File "/usr/lib/python3.6/concurrent/futures/_base.py", line 425, in result
    return self.__get_result()
  File "/usr/lib/python3.6/concurrent/futures/_base.py", line 384, in __get_result
    raise self._exception
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/tenacity/__init__.py", line 407, in __call__
    result = fn(*args, **kwargs)
  File "/home/ubuntu/src/review.opendev.org/openstack/charm-neutron-gateway/.tox/func-target/lib/python3.6/site-packages/zaza/openstack/charm_tests/neutron/tests.py", line 152, in _validate_openvswitch_agent_qos
    self.assertIn('qos', ovs_agent['configurations']['extensions'])
AssertionError: 'qos' not found in []

[Alex Kavanagh (ajkavanagh)]

This is almost certainly a duplicate of: https://bugs.launchpad.net/neutron/+bug/1929676 -- which is is a neutron bug. Review on neutron for backport to wallaby: https://review.opendev.org/c/openstack/neutron/+/812509