Extract standard storage responses test helpers

There are a limited number of responses from the API we test and they
were duplicated. This cuts down on the duplication.
Fix authentication loops

The Orbit middleware does not differentiate between bad credentials or
expired credentials. In either case the response is 401.

That means by rescuing and returning `nil` within authentication
requests triggered by standard requests we could enter a loop when the
credentials were incorrect.
Merge pull request #9 from brightbox/prevent_storage_auth_loop

Prevent storage authentication loop