Add virtio-scsi bus support for bdm

Add support to use virtio-scsi controller when booting from a cinder
volume which is created from a glance image set with "virito-scsi"
hw_scsi_model property.

blueprint add-virtio-scsi-bus-for-bdm

Change-Id: I76a01d5cdb4e72d5121de0d821152102bc9d4fb2
Merge "Add virtio-scsi bus support for bdm"