[Reviewer: Alex] Fix backups with new schema

Alex,

Please can you review my fix to backups to backup on a per-keyspace basis.  The key change is that we parse the `provisioning` or `cache` out of the keyspace name (if present) and add this as an additional level in the backup hierarchy.  I've made corresponding updates to the backup documentation.

A fix to chef will follow shortly.

Thanks,

Matt