dog/vdi: add data object reference support to vdi list command

Once I found the error message in sheep.log:

recover_replication_object(412) can not recover oid 3d211c0000025a

And I do want to know the data object is referenced by which vdi
or vdis. It seems no command support it, so I create a new one.

Usage: dog vdi list -o <oid>

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>