[OpenStackAnsible] Transition Ussuri to EM

This transition the ussuri branch to extended maintenance.
Changes for bugfixes and things the team deems important are
still encouraged, but there will no longer be official releases
off of the branch.

Please +1 if the team is ready for us to proceed with this
transition, or -1 if there are any final backports currently in
flight that we should wait for. For the latter case, please
update the patch with the new commit hash after doing a final
release to get those changes out so we know to proceed with the
transition.

Change-Id: If96dfdba1c04f88b882d897a097997b868e5ff15

deliverables/ussuri/openstack-ansible.yaml

@@ -89,6 +89,10 @@ releases:
     projects:
       - repo: openstack/openstack-ansible
         hash: 9f1ac5f572679b66c426ce5762816acbe2250fc0
+  - version: ussuri-em
+    projects:
+      - repo: openstack/openstack-ansible
+        hash: 9f1ac5f572679b66c426ce5762816acbe2250fc0
 branches:
   - name: stable/ussuri
     location: 21.0.0.0rc1