[mistral] Transition Stein to EM

This transition the stein 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: I483bfa4a2bd0307e73d3a33d96e7245b2d19f588

deliverables/stein/python-mistralclient.yaml

@@ -15,6 +15,10 @@ releases:
       - hash: 1712bd4b6c698f5eff783e07c5f69b475c12c24d
         repo: openstack/python-mistralclient
     version: 3.8.1
+  - version: stein-em
+    projects:
+      - repo: openstack/python-mistralclient
+        hash: 1712bd4b6c698f5eff783e07c5f69b475c12c24d
 branches:
   - location: 3.8.0
     name: stable/stein