collie: add new commands to manipulate multi-disks

Three command added:
 $ collie node md info # show information about md of {this node, all nodes}
 $ collie node md plug path1,{path2,...} # plug disk(s) into node
 $ collie node md unplug path1,{path2,...} # unplug disk(s) into node

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: remove duplicate recovery complete notification

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
tsets: add 057 to test md hot-plug and hot-unplug

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: teach journal file to be md friendly

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
tests/047: add md test support

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: teach journal file to handle epoch and config write

journal_write_epoch and journal_write_confi is a placeholder for future use.

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: use new journal API for config file

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>
sheep: rename journal_file.c as journal.c

Signed-off-by: Liu Yuan <tailai.ly@taobao.com>