neutron-ovs-cleanup currently ships with an outdated path to the plugin configuration:

======
# cat /etc/systemd/system/multi-user.target.wants/neutron-ovs-cleanup.service
[Unit]
Description=OpenStack Neutron Open vSwitch Cleanup Utility
After=syslog.target network.target openvswitch.service
Before=neutron-openvswitch-agent.service neutron-dhcp-agent.service neutron-l3-agent.service openstack-nova-compute.service

[Service]
Type=oneshot
User=neutron
ExecStart=/usr/bin/neutron-ovs-cleanup --config-file /usr/share/neutron/neutron-dist.conf --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-ovs-cleanup --log-file /var/log/neutron/ovs-cleanup.log
ExecStop=/usr/bin/neutron-ovs-cleanup --config-file /usr/share/neutron/neutron-dist.conf --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-ovs-cleanup --log-file /var/log/neutron/ovs-cleanup.log
PrivateTmp=true
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
======

This will lead neutron-ovs-cleanup to fail:
======
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: File "/usr/bin/neutron-ovs-cleanup", line 10, in <module>
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: sys.exit(main())
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: File "/usr/lib/python2.7/site-packages/neutron/cmd/ovs_cleanup.py", line 83, in main
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: conf()
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: File "/usr/lib/python2.7/site-packages/oslo_config/cfg.py", line 1887, in __call__
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: raise ConfigFilesNotFoundError(self._namespace._files_not_found)
Oct 09 15:32:08 test-dmsimard.novalocal neutron-ovs-cleanup[17595]: oslo_config.cfg.ConfigFilesNotFoundError: Failed to find some config files: /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini
Oct 09 15:32:09 test-dmsimard.novalocal systemd[1]: neutron-ovs-cleanup.service: main process exited, code=exited, status=1/FAILURE
Oct 09 15:32:09 test-dmsimard.novalocal systemd[1]: Failed to start OpenStack Neutron Open vSwitch Cleanup Utility.
Oct 09 15:32:09 test-dmsimard.novalocal systemd[1]: Unit neutron-ovs-cleanup.service entered failed state.
======

The configuration for the plugins is in /etc/neutron/plugins/ml2/ now.