distgit: Block push of branches named 'origin/*'

We already use the update hook for gitolite.

This introduces a new update hook, which merely chains the gitolite one,
and a new one to block pushes to badly named branches.

The new hook was written originally by Till Maas.

https://fedorahosted.org/rel-eng/ticket/4071

roles/git/hooks/files/update-block-push-origin

@@ -0,0 +1,10 @@
+#!/bin/sh
+#
+# Block pushes to branches if their name starts with `origin/`
+# https://fedorahosted.org/rel-eng/ticket/4071
+
+refname="${1}"
+sha1_old="${2}"
+sha1_new="${3}"
+
+echo "${refname}" | grep -qE '^refs/heads/origin/' && exit 1 || exit 0