[Rackspace] Updated compute_v2, storage, and cdn services to support auth 2.0

I updated compute_v2, storage, and cdn services to do authorization using the Identity service by default. (The identification service uses auth 2.0 endpoints) Services will fallback to the old  legacy authentication system if supplied with an old 1.0/1.1 authorization endpoint via the `:rackspace_auth_url` parameter.

I have added a ServiceCatalog model to the Identify service. This model is populated when a user uses `Identify#authenticate`. The service catalog is returned by `Identify#service_catalog`.

Regions should now be selected by using the `:rackspace_region` parameter along with the value of `:dfw`, `:ord`. `:lon`. (Note these values are generated off of the service catalog returned from the auth 2.0 request.) A deprecation warning will appear if user specifies compute_v2 region using `:rackspace_endpoint` along with one of the following constants: `DFW_ENDPOINT`, `ORD_ENDPOINT`, `LON_ENDPOINT`. 

User's are able to manually select endpoints by using one of the following values: `:rackspace_storage_url`, `rackspace_cdn_url`, and `:rackspace_compute_url`. A deprecation warning is displayed if user specifies compute_v2 endpoint using `rackspace_endpoint`. (This was in attempt to standardize how you specify endpoints for each service.)