Reviewer Matt: Enhance backup

Enhancement to crest backup scripts to copy across (hard link) Cassandra backup files outside the Cassandra tree.

Also fixes up permission on backup files when copying them back into place.

The backup process locally should be exactly the same as before, but the remote backup process is simplified, namely:
  - You can now directly copy the files off the machine from say /usr/share/clearwater/homestead/backup/backups
  - When restoring or listing backups you can provide a directory to backup from, so that files that have been scp'd onto the box can be used directly, eliminating the need to copy them into place first

I've tested this by running the backup script over a Homestead Cassandra db on my local machine, verifying that data is restored as expected. I've also scp'd the data off the machine, truncated the db and then re-uploaded the backup files, restored from this separate location and made sure the data is restored.