libguestfs.tests: Recover to vdx if listed disk is virtio.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libguestfs.tests: Make vm is down before testing.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
guestfish.tests: Fix wrong vm setting for cloned vm.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libguestfs.tests: Check only volume name in vm.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>