[Rackspace | Storage] Mocks for the Storage service

Hello! I've created mocks for all of the Rackspace Storage requests, as well as mocking the Identity service's `create_token` request and a little adjustment in the CDN service to support them. I now get a clean run of all tests in `tests/rackspace/requests/storage/`, `tests/rackspace/models/storage/`, and `tests/rackspace/storage_tests.rb` with all of the `pending if Fog.mocking?` guards removed.