tests: Change the python interpreter directive

This makes the script check the environment for the current python
interpreter in use instead of assuming that the python executable points
to a python 2 interpreter.

Signed-off-by: Roger Zanoni <roger.zanoni@openbossa.org>

tests/hwsim/run-tests.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python2
 #
 # AP tests
 # Copyright (c) 2013-2014, Jouni Malinen <j@w1.fi>