[winstackers] 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: I47cbb52f9865f244d09ffcfd75736c556191865f

deliverables/stein/networking-hyperv.yaml

@@ -19,6 +19,10 @@ releases:
       - hash: dd15b0e6c4b553b7120aa06054cfce5010e7c304
         repo: openstack/networking-hyperv
     version: 7.2.1
+  - version: stein-em
+    projects:
+      - repo: openstack/networking-hyperv
+        hash: dd15b0e6c4b553b7120aa06054cfce5010e7c304
 branches:
   - location: 7.1.0
     name: stable/stein

deliverables/stein/os-win.yaml

@@ -23,6 +23,10 @@ releases:
       - hash: 027749c401a73f4561d8542cdcaf5672ac9f4ee2
         repo: openstack/os-win
     version: 4.2.1
+  - version: stein-em
+    projects:
+      - repo: openstack/os-win
+        hash: 027749c401a73f4561d8542cdcaf5672ac9f4ee2
 branches:
   - location: 4.2.0
     name: stable/stein