virsh.vol_create: Update and extend cases

1. Test create 128 partition volume on disk pool(gpt disk)
2. Create thin lvm pool/volume in libvirt logical pool
3. Create snapshopt volume in libvirt logical pool
4. Deactivate volume in libvirt logical pool
5. Use invalid target path('/dev/') to create pool/volume, which should pass
6. Use 'qemu-img' to cretae vmdk v4/v5 images in libvirt dir pool

Signed-off-by: Yanbing Du <ydu@redhat.com>