libvirt.tests: Add virsh domblklist test

v1:
Add virsh domblklist test and cfg

v2:
Change detach-disk on running domain with --config flag when use
domblkinfo with --inactive flag, this change is due to bug 1049529
fixed the --config flag problem when domain is running

v3:
Replace disk_type with type_name

Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #4 from waynesun09/virsh_domblklist

libvirt.tests: Add virsh domblklist test