Use /usr/bin/env python to autodetect python

https://review.openstack.org/566284 used
/bin/python as the shebang but this can be different
for different platforms, switch to /usr/bin/env to
handle it.

Change-Id: Id915ded03ae5a471ffa2dca13e2da90021279f63
(cherry picked from commit 247438dd5a)

extraconfig/tasks/instanceha/check-run-nova-compute

@@ -1,4 +1,4 @@
-#!/bin/python -utt
+#!/usr/bin/env python -utt
 
 import os
 import sys