Add tripleo-ui to the list of gated projects
Add tripleo-ui to the list of gated projects

Adding openstack/tripleo-ui to the PROJECTS variable to be properly
cloned to the change to test ref, or it will not be gated

Closes-Bug: 1657416
Change-Id: I7fb55e122ca0d0932a3240d414295f9f8bd6ce53

openstack-infra/project-config,openstack-infra/project-config