Initial commit of rax library

This library provides functionality for the Rackspace Public Cloud by
way of the official pyrax SDK (https://github.com/rackspace/pyrax). At
this time only the cloudservers service is functional. Instances can be
created or deleted. Idempotency is provided on matching instances with
the same name, flavor, image, and metadata values within a given
region.

pyrax usage does require a credentials file written out to hold username
and API key.  See pyrax documentation for details
(https://github.com/rackspace/pyrax/blob/master/docs/pyrax_doc.md)
Initial commit of rax inventory plugin

The rax inventory plugin provides a way to discovery inventory in the
Rackspace Public Cloud by way of pyrax, the official SDK. Grouping will
be done if a group:name is found in the instance metadata. When a single
host is queried all the instance details are returned with a rax_
prefix.

Because inventory plugins cannot take extra arguments, ENV variables
must be set to point to the pyrax compatible credentials file and the
region to query against.
Fix up docs and add ability to insert files

Files can be inserted during server creation (like a fully formed
authorized_keys file). This code allows that to happen.

Docs were updated for formatting, location, and to add the new entry for
files.
Merge pull request #2537 from j2sol/rax

Provide functionality to work with Rackspace's public cloud