Add "mr pullup" subcommand to pull updates from upstream repos

.mrconfig

+[DEFAULT]
+git_pullup = "$(dirname "$MR_CONFIG")/bin/pull-from-upstream"
+
 [swh-site]
 checkout = git clone https://forge.softwareheritage.org/source/puppet-swh-site.git swh-site \
 	 && cd swh-site \

bin/pull-from-upstream

+#!/bin/bash
+
+set -e
+
+if [ -d .git/refs/remotes/upstream ]; then
+    git fetch upstream
+
+    oldbranch=$(git rev-parse --abbrev-ref HEAD)
+
+    if [ "$oldbranch" != "master" ]; then
+        git checkout master
+    fi
+
+    git merge upstream/master
+    git push origin master:master --tags
+
+    if [ "$oldbranch" != "master" ]; then
+        git checkout $oldbranch
+    fi
+fi