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.

contrib/inventory/brook.ini

@@ -1,4 +1,3 @@
-#!/usr/bin/python
 # Copyright 2016 Doalitic.
 #
 # This file is part of Ansible

contrib/inventory/cloudforms.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 # vim: set fileencoding=utf-8 :
 #
 # Copyright (C) 2016 Guido Günther <agx@sigxcpu.org>

contrib/inventory/gce.ini

@@ -1,4 +1,3 @@
-#!/usr/bin/python
 # Copyright 2013 Google Inc.
 #
 # This file is part of Ansible

contrib/inventory/nsot.py

@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python
 
 '''
 nsot

contrib/inventory/rackhd.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 import json
 import requests

contrib/inventory/spacewalk.py

@@ -1,4 +1,4 @@
-#!/bin/env python
+#!/usr/bin/env python
 
 """
 Spacewalk external inventory script