sheep/md: fix dog cluster info command show wrong disk number

If we enable diskvnodes mode and encounter EIO, running dog
cluster info will show wrong disk number in the new epoch.
We should update node disks when handling EIO and unplug the
disk.

Signed-off-by: Bingpeng Zhu <bingpeng.zbp@alibaba-inc.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>