vhost-user-blk device (booted VMs)

[kalyazin]

Feature Request

Add support for vhost-user-blk devices by leaving snapshotting support for vhost-user-blk out of scope.

Describe the desired solution

Firecracker implements a vhost-user-blk frontend.

Describe possible alternatives

Existing virtio block device.

Additional context

NA

Checks

• [x] Have you searched the Firecracker Issues database for similar requests?
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• [x] Have you read and understood Firecracker's core tenets?