[rackspace] Adding Default UUID Queue Name

Based on my conversation with @brianhartsock here https://github.com/fog/fog/pull/2237#issuecomment-26021181, I have decided that it's a much better approach to generate a UUID if a client id has not been specified rather than my previous approach of only adding a client id in testing.

In order to implement this, I had to add a UUID library. The google-api-tools gem uses uuidtools, so I decided that I would just stick with that. Do you mind adding an additional dependency @geemus? 

On a side note, it looks like the queueing service has been updated to expect a UUID for a client id, so my previous approach would have failed anyways!