TARGET_DISK needs robustness.

[jason-oliveira]

As referenced in #1, TARGET_DISK has no way of telling between NVME, eMMC, IDE/SATA/SCSI, and virtual drives.

if ROOT_PASSWORD is set, /dev/{sda/nvme0n1/mmcblk0) can be detected via testing with lsblk, and TARGET_DISK can be modified accordingly. else, throw an error if none are found or warn if /dev/vda is found.

[jason-oliveira]

After giving this more thought, it would be best to give an unset TARGET_DISK="" at the top of the config, with instructions on default values if they want to override, then later on:

Check value of TARGET_DISK, and if unset:
If ROOT_PASSWORD is also unset, assume /dev/vda.
If ROOT_PASSWORD is set, use lsblk to see what they actually have, and presume the first disk found, unless both sda and either /nvme0n1 or mmcblk0 exist, then assume the latter (sda is usually USB).