Clean up shebangs for various files.

- Remove shebangs from:
  - ini files
  - unit tests
  - module_utils
  - plugins
  - module_docs_fragments
  - non-executable Makefiles
- Change non-modules from '/usr/bin/python' to '/usr/bin/env python'.
- Change '/bin/env' to '/usr/bin/env'.

Also removed main functions from unit tests (since they no longer
have a shebang) and fixed a python 3 compatibility issue with
update_bundled.py so it does not need to specify a python 2 shebang.

A script was added to check for unexpected shebangs in files.
This script is run during CI on Shippable.

test/units/plugins/action/test_action.py

@@ -1,4 +1,3 @@
-#!/usr/bin/env python
 # -*- coding: utf-8 -*-
 # (c) 2015, Florian Apolloner <florian@apolloner.eu>
 #