sheep: remove nr_copies parameter

We have a vdi_copy tree and we can get the vdi copy information for the tree
on the fly, no need to get it from inode.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: unify snapid passing and put it in vdi_iocb

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: pass vdi_iocb for vdi deletion

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: refactor vdi lookup, create, delete operation

This patch set only refactor vdi code of the sheep side, so try to maintain
the same behavior as old code and (should) passes all the tests regarding
VDI operation.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
tests/039: fix the output for the refactored vdi code

Highest snapid is internally used by SD for the next snapshot, it should means
not exist for users. So we should NO_TAG if users want to access with this
invalid tag.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>