Comment 1 for bug 1808506

As an example of the error, when using the multi-pool driver, upon a kuryr-controller restart, trying to recover the precreated neutron ports will fail with:
2018-12-13 16:31:53.328 1 ERROR oslo_service.service [-] Error starting thread.: TypeError: sequence item 0: expected string, NoneType found
2018-12-13 16:31:53.328 1 ERROR oslo_service.service Traceback (most recent call last):
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/oslo_service/service.py", line 796, in run_service
2018-12-13 16:31:53.328 1 ERROR oslo_service.service service.start()
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/kuryr_kubernetes/controller/service.py", line 112, in start
2018-12-13 16:31:53.328 1 ERROR oslo_service.service self.pool_driver.sync_pools()
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/kuryr_kubernetes/controller/drivers/vif_pool.py", line 855, in sync_pools
2018-12-13 16:31:53.328 1 ERROR oslo_service.service vif_drv.sync_pools()
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 328, in inner
2018-12-13 16:31:53.328 1 ERROR oslo_service.service return f(*args, **kwargs)
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 328, in inner
2018-12-13 16:31:53.328 1 ERROR oslo_service.service return f(*args, **kwargs)
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/kuryr_kubernetes/controller/drivers/vif_pool.py", line 299, in sync_pools
2018-12-13 16:31:53.328 1 ERROR oslo_service.service self._recover_precreated_ports()
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/kuryr_kubernetes/controller/drivers/vif_pool.py", line 416, in _recover_precreated_ports
2018-12-13 16:31:53.328 1 ERROR oslo_service.service vif = ovu.neutron_to_osvif_vif(vif_plugin, port, subnet)
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/kuryr_kubernetes/os_vif_util.py", line 347, in neutron_to_osvif_vif
2018-12-13 16:31:53.328 1 ERROR oslo_service.service name=vif_translator, invoke_on_load=False)
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/stevedore/driver.py", line 61, in __init__
2018-12-13 16:31:53.328 1 ERROR oslo_service.service warn_on_missing_entrypoint=warn_on_missing_entrypoint
2018-12-13 16:31:53.328 1 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/stevedore/named.py", line 88, in __init__
2018-12-13 16:31:53.328 1 ERROR oslo_service.service ', '.join(self._missing_names))
2018-12-13 16:31:53.328 1 ERROR oslo_service.service TypeError: sequence item 0: expected string, NoneType found
2018-12-13 16:31:53.328 1 ERROR oslo_service.service