With the new ``neutron_ovn_availability_zones`` parameter it is possible
to define network availability zones for OVN. Further details can be found
in the Neutron OVN documentation:
https://docs.openstack.org/neutron/latest/admin/ovn/availability_zones.html#how-to-configure-it

Change-Id: I203e0d400a3218d0b4a41f2a948207032c4febec