[CA-137573]: Fix "Unrecognised bus type" VDIs.

Use "device/subsystem" to obtain SCSI details of the host CDROM drive.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Chandrika Srinivasan <chandrika.srinivasan@citrix.com>
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

(cherry picked from commit 6ad534df70013f8f24dbf3f7d646694f606702a6)