Arbitrary ephemeral mount point detection/override

[alfpark]

Batch now supports arbitrary ephemeral mountpoints. Remove instances of hardcoded ephemeral mountpoint:

• [ ] Mountpoint override/hint in pool.yaml?
• [ ] Detect ephemeral disk settings in nodeprep
  • [x] Ephemeral device/partition
  • [x] Mount point
  • [ ] Persist to table using cascade?
• [ ] Update refs from settings
• [ ] Align mounts with native support