Add job to propose tag merges

With pbr tag-based versioning, not having the latest release tag in the
master branch makes the output a little nasty. Add a job that makes a
merge commit containing the tag on a release from milestone-proposed
branch. The merge strategy it uses is 'ours' because we're not
attempting to use this to keep code lines up to date - the expectation
is that content added in milestone-proposed should already be in master.
The main thing we want to do is re-connect the revision and tag history
with master, so that things like 'git tag --contains' work.

Closes-Bug: 1192039
Change-Id: I06c06bd7542ae493e74fdcaa3c4419f84843cd03

files/slave_scripts/merge_tags.sh

@@ -0,0 +1,27 @@
+#!/bin/bash -xe
+
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+TAG=$1
+
+git config user.name "OpenStack Jenkins"
+git config user.email "jenkins@openstack.org"
+git config gitreview.username "jenkins"
+
+git review -s
+git checkout master
+git reset --hard origin/master
+git merge -s ours $TAG
+# Get a Change-Id
+GIT_EDITOR=true git commit --amend
+git review -R -t merge/release-tag