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_policy_id')
- 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.
Story: 2004602
Task: 28512
Change-Id: Ie974afa52fe70cbab72b7e7f75bf7ee1015e148c
e0c45ce4d2