[rackspace] Reauthenticate and retry request when authentication token expires

This pull request is the result of a carrierwave bug report where the Rackspace provider in fog was throwing a HTTP 401 after a rails application had been running of over 24 hours. As a result of that bug, I created https://github.com/fog/fog/pull/1899.

It turns out that this issue is present in most of the Rackspace services. This pull request replaces PR #1899 with a much more comprehensive fix for the issue and refactors all of the services `request` methods to the `Fog::Rackspace::Service` class with the hope of a much more common handling of requests.