libvirt: Add test module for virsh domblkinfo.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virt: Add virsh function for virsh domblkinfo.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virt: Add get_disk_source() for virsh domblkinfo.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libvirt: fix a bug for virsh domblkinfo

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libvirt: Avoid size check if disk format isn't 'raw'.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Merge pull request #318 from liyangfnst/domblkinfo

Add test for virsh domblkinfo v4