Set shebang line of zuul-cloner script

To run a script in a virtualenv, you need to us the python in the
virtualenv. This script needs things (yaml) that arent' on the base
system but instead are only in the virtualenv.

Change-Id: Ic915c4db30814b7deefd8adc234df594d1eb20fa

roles/fetch-zuul-cloner/templates/zuul-cloner-shim.py.j2

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!{{ destination | dirname }}/python
 # Copyright 2017 Red Hat
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may