vmspawn previously hardcoded virtio-blk for all drives. This adds
--image-disk-type= to select the root disk type (virtio-blk,
virtio-scsi, or nvme) and allows per-drive overrides via a
colon-separated prefix on --extra-drive=. The format and disk type
prefixes can appear in any order since their value sets don't overlap.
For virtio-scsi, a single shared controller is created with drives
attached as scsi-hd devices. For nvme, each drive gets its own
controller. Both have serial number length limits (30 and 20 characters
respectively), so long filenames are replaced with a truncated SHA-256
hex digest.
Lennart Poettering
fb17ad1581