Add func test to validate baymodel-update referenced by bay
Add func test to validate baymodel-update referenced by bay

This patch https://review.openstack.org/#/c/266420/ disallowed
baymodel-update when it is referenced by bay(s).
For regression, add to have func test coverage for that.

Change-Id: I4db767da900e48af0234bded3aaf371557c0bfcd
Closes-Bug: #1533746

ArchiFleKs/magnum,ArchiFleKs/magnum,jay-lau/magnum,openstack/magnum,openstack/magnum