This adds revises_on_change for the following models
and API tests to ensure the correct behavior:
* port security (network and port)
* DNS domain (network and port)
* extra dhcp opts (port)
* extra routes (router)
* subnet service type (subnet)
Additionally, it configures the DNS extension to be loaded
in the gate since the extension is enabled for tempest.
Closes-Bug: #1627649
Change-Id: Ifa969c8c2582f8f41d42df07652f259781a36bb5
971cf85034