ansible: Add Rackspace cloud support via pyrax module

Note: This currently doesn't work. I think I've added everything correctly, but when trying to install it I see:

```
==> Downloading https://pypi.python.org/packages/source/p/pyrax/pyrax-1.8.0.tar.gz
Already downloaded: /Library/Caches/Homebrew/ansible--pyrax-1.8.0.tar.gz
==> python setup.py install --prefix=/usr/local/Cellar/ansible/1.6.1/libexec
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/setuptools/__init__.py", line 53, in __init__
    _Command.__init__(self,dist)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/cmd.py", line 59, in __init__
    raise TypeError, "dist must be a Distribution instance"
TypeError: dist must be a Distribution instance

READ THIS: https://github.com/Homebrew/homebrew/wiki/troubleshooting
```