Backup client fails if backup directory starts with same string as Stash home

The backup client dies if it thinks the backup directory is in Stash home. Unfortunately, the detection is string-based. For instance, the following fails:

Stash home: /opt/stash
Backup home: /opt/stash-backups

Both paths start with /opt/stash even though stash-backups is a different directory.

The backup client should be walking the directory structure instead of just doing a string compare.