sheepdog proto: add block_size_shift member to sheepdog internal data.

This patch adds a information of block_size_shift
to sheepdog request, response, state.

Signed-off-by: Teruaki Ishizaki <ishizaki.teruaki@lab.ntt.co.jp>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
sheep, dog: add "block_size_shift" option to cluster format command

This patch changes for specifying cluster default block_size_shift.

Signed-off-by: Teruaki Ishizaki <ishizaki.teruaki@lab.ntt.co.jp>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
sheep, dog: add selectable object_size support of VDI operation

Data object size was fix to 4MB and not selectable.
This patch add feature to select data object size of VDI.

If you want to use 8MB(2^23) data object_size, specify the
block_size_shift bit num to 23.

ex) dog vdi create -z 23 testvdi 100M

Signed-off-by: Teruaki Ishizaki <ishizaki.teruaki@lab.ntt.co.jp>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>