Revert shebang python executable name from python3 back to python. World is...

Revert shebang python executable name from python3 back to python. World is not yet ready for this change.

warden_filer/warden_filer.py

-#!/usr/bin/python3
+#!/usr/bin/python
 # -*- coding: utf-8 -*-
 #
 # Copyright (C) 2011-2015 Cesnet z.s.p.o