From Image Meta Properties: hw_cdrom_bus=scsi, and use virtio-scsi mode,
it will also need a disk address for it. So we need to calculate the
disk address when call the function to get the next unit of scsi controller.
Closes-Bug: #1867075
Change-Id: Ifd8b249de3e8f96fa13db252f0abe2b1bd950de0
Signed-off-by: Kevin Zhao <kevin.zhao@linaro.org>
(cherry picked from commit c8d6767cf8)
(cherry picked from commit 11b2b7f0b3)
(cherry picked from commit 86328d1146)
(cherry picked from commit 3b2c6ccf26)