[Puppet OpenStack] Transition Train to EM

This transition the train 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: Ib0ea7e3976c48fc5d5334b3b0a7b37a3dae23d66

deliverables/train/puppet-heat.yaml

@@ -26,6 +26,10 @@ releases:
     projects:
       - repo: openstack/puppet-heat
         hash: 31e48ae3649a5245b3f33be3b18f586cf090e1eb
+  - version: train-em
+    projects:
+      - repo: openstack/puppet-heat
+        hash: 31e48ae3649a5245b3f33be3b18f586cf090e1eb
 branches:
   - name: stable/train
     location: 15.4.0