Set default neutron availability zone (#2605)

Set the default availability zone for neutron to the configured `nova`
zone. OVN external ports require the availablity zone to be set if zones
are configured. Failure to do so will result in an empty
`ha_chassis_group`. Setting the zone via `availability-zone-hint` is not
supported by ansible module `openstack.cloud.network`.

Part of osism/issues#1196

Signed-off-by: Jan Horstmann <[email protected]>

Author: janhorstmann

environments/kolla/files/overlays/neutron.conf

@@ -1,2 +1,3 @@
 [DEFAULT]
 global_physnet_mtu = 1400
+default_availability_zones = nova