Use /usr/bin/python2

Part of the effort to port FreeIPA to Arch Linux,
where Python 3 is the default.

FreeIPA hasn't been ported to Python 3, so the code must be modified to
run /usr/bin/python2

https://fedorahosted.org/freeipa/ticket/3438

Updated by pviktori@redhat.com

setup.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 
 # Authors:
 #   Jason Gerard DeRose <jderose@redhat.com>