Squashed changes:
- Use 'inventory' instead of 'hostfile' in ansible.cfg.
'hostfile' is deprecated.
- Use 'os.environ.copy()' in zuul_return.py since this causes 2.4 to
throw an exception now deep within module.exit_json().
Change-Id: I0a52c9e169a54d24a7b361010045fb10211418b7