The project/endpoint should be set in the original (non-as_ref'd) creds,
because we call `wake_compute` not only in `try_password_hack` but also
later in the connection retry logic.
This PR also removes the obsolete `as_ref` method and makes the code
simpler because we no longer need this complication after a recent
refactoring.
Further action points: finally introduce typestate in creds (planned).
96e78394f5