This adds four options for virsh command attach-disk.

--cache option allows user to specify cache mode of disk device
from virsh command line when attaching a disk device.

--serial option allows user to specify serial string of disk device
from virsh command line when attaching a disk device.

--shareable option allows user to specify whether the disk device is
shareable between domains when attaching a disk device from virsh
command line.

--address option allows user to specify address of disk device when
attaching a disk device.