Extend tests for external DNS integration

- Verify records are deleted on server/fip deletion
- Verify records are created for ports on special networks
  (Use case 3 in [0])
- Verify the new subnet-dns-publish-fixed-ip extension works as designed

[0]
https://docs.openstack.org/neutron/latest/admin/config-dns-int-ext-serv.html

Depends-On: https://review.opendev.org/662409
Change-Id: Id7b799904f45ac2e3f913c6201aa33afef896af0
2 files changed