Improved mount_volume -> local_storage role.

Renamed mount_volume role into local_storage role.
Replaced disabled defaults with a README.md
Renamed variables:
- volume_group_folders into local_mount_subfolders: and changed the logic to support creating other sub folders not specifically for groups too.
- volumes into local_mounts.
Fixed bug that caused bind mounts to fail.
Fixed wrong mode for /local on dragen compute nodes.

rug-cit-hpc / league-of-robots