add copied version __dog_vdi from __qemu_img

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
first version of __dog_vdi

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
catch unsupported state cases in __dog_vdi und __qemu_img

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
cleanups

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
++changes

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>