CA-136790: Ensure consistent behaviour of get_devices_by_SCSIid

Dependant on the udev rules there may be a mapper device in by-scsid. This
commit ensures that that get_devices_by_SCSIid never returns the mapper-device.

Signed-off-by: Robert Breker <robert.breker@citrix.com>
CA-136790: scsiutil.getdev should return dm-x instead of individual paths

when handling mapper devices.

Signed-off-by: Robert Breker <robert.breker@citrix.com>