Load balancers were going in to ERROR when updating vip_qos_policy_id in
two different cases:
- QoS extension enabled: the VIP DB data model was incorrectly
constructed ('vip_qos_policy_id' where it should have been
- QoS extension disabled: setting an UUID or None would fail in the LB
update flow as the extension is disabled, and the API would return
HTTP 202 to the user.
(cherry picked from commit e0c45ce4)