Reinstate Rackspace support - WIP

Following v1.25.0, Rackspace support was extracted into a module however
it broke support to the original fog API.

The Rackspace module is currently disabled until a few key files are
replaced.

This adds tests that worked against v1.25.0 that checks that `rackspace`
is registered correctly. See https://github.com/fog/fog/pull/3326

This reverts commit 9717002fd3d18aef0c359fc52ac704894a34dac0.