Neutron-api container fails to start on bootstrap controller after upgrade

Issue

• After upgrading the bootstrap controller, the neutron-api container fails to start with the following error:

+ echo 'Running command: '\''/usr/bin/neutron-server --config-file /usr/share/neutron/neutron-dist.conf --config-dir /usr/share/neutron/server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-server --log-file=/var/log/neutron/server.log'\'''
Running command: '/usr/bin/neutron-server --config-file /usr/share/neutron/neutron-dist.conf --config-dir /usr/share/neutron/server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-server --log-file=/var/log/neutron/server.log'

+ exec /usr/bin/neutron-server --config-file /usr/share/neutron/neutron-dist.conf --config-dir /usr/share/neutron/server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-server --log-file=/var/log/neutron/server.log
Traceback (most recent call last):
File "/usr/bin/neutron-server", line 10, in <module>
sys.exit(main())
File "/usr/lib/python3.6/site-packages/neutron/cmd/eventlet/server/__init__.py", line 19, in main
server.boot_server(wsgi_eventlet.eventlet_wsgi_server)
File "/usr/lib/python3.6/site-packages/neutron/server/__init__.py", line 66, in boot_server
_init_configuration()
File "/usr/lib/python3.6/site-packages/neutron/server/__init__.py", line 56, in _init_configuration
config.init(sys.argv[1:], default_config_files=conf_files)
File "/usr/lib/python3.6/site-packages/neutron/common/config.py", line 89, in init
**kwargs)
File "/usr/lib/python3.6/site-packages/oslo_config/cfg.py", line 2134, in __call__
raise ConfigFilesNotFoundError(self._namespace._files_not_found)
oslo_config.cfg.ConfigFilesNotFoundError: Failed to find some config files: /etc/neutron/plugin.ini