Propagate auth mechanism/backend failures to filesystem layer

Failure to prepare the storage during backend or auth mechanism
manipulation will throw an InsufficientDataForMeaningfulAnswerException,
which is propagated to StorageNotAvailableException in the filesystem
layer via the FailedStorage helper class.

When a storage is unavailable not due to failure, but due to
insufficient data being available, a special 'indeterminate' status is
returned to the configuration UI.