Release horizon for stable/stein

This release picks up new commits to horizon since
the last release from stable/stein.

This is being proposed as a convenience to help make sure stable
changes are being released. If the team is good with this going out,
please respond with a +1 to let the release team know it is OK to
proceed.

If it is not wanted at this time, or if there are more changes that
would be good to get merged before doing a  stable release, please
leave a -1 with a comment with what the team would prefer. We can
then either abandon this patch, or wait for an update with a new
commit hash to use instead.

This is not a release team activity, it is just to help out with
stable releases. If there is no response to the patch, we will
assume a release is not needed and abandon the patch after one
week.

Change-Id: If013d4d1ecec13d1b6d5c09e5f1888d4c60a91a8
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

deliverables/stein/horizon.yaml

@@ -41,6 +41,10 @@ releases:
     projects:
       - repo: openstack/horizon
         hash: 6b32ff44ea88772a2b9b668e6efa9181058c2f02
+  - version: 15.3.1
+    projects:
+      - repo: openstack/horizon
+        hash: 8da0dcd21200cc851e57de4dfa46c3c838c73c3c
 repository-settings:
   openstack/horizon: {}
 branches: