fuel-qa: ubuntu-xenial gates excluded for stable/mitaka and older
fuel-qa: ubuntu-xenial gates excluded for stable/mitaka and older

ubuntu-xenial gates should be excluded for stable/mitaka and older
Xenial jobs should be run for newton (current master) and newer

Change-Id: I1dd1c87b1a3d75d6d25877afc93a5730cdd4bbf3

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