Add virsh desc function wrapper

Signed-off-by: Yanbing Du <ydu@redhat.com>
Add cfg file for virsh desc testing

Signed-off-by: Yanbing Du <ydu@redhat.com>
Add test module for virsh desc testing

Signed-off-by: Yanbing Du <ydu@redhat.com>
Fix several problems in PR#786

Signed-off-by: Yanbing Du <ydu@redhat.com>