Don't run gate-cinder-tox-db-functional on stable/liberty
Don't run gate-cinder-tox-db-functional on stable/liberty

Functional tests do not exist on stable/liberty, so do not
run them.

Change-Id: I0b582ac2c7c227faf72bf701dfa88e83a8ba9ee6
Closes-Bug: #1602024

dongwenjuan/project-config,Tesora/tesora-project-config,dongwenjuan/project-config,openstack-infra/project-config,openstack-infra/project-config,Tesora/tesora-project-config