[Sheepdog] refinement of shepherd commands

[MORITA Kazutaka]

Hi all,

I think of changing shepherd commands syntax because current syntax is
confusing; we run `shepherd info -t dog' to list sheepdog nodes but we
don't call the server process `dog' now, and we run `shepherd mkfs' to
format sheepdog storage but sheepdog is not a regular file system.

My suggestion of the new shepherd usage is as follows:

==
shepherd command [command options]

Command list:
  vdi-info              show virtual disk image information
  vdi-delete            delete a vdi
  vdi-list              list vdis
  vdi-lock              lock a vdi (for debug)
  vdi-release           release a vdi (for debug)
  vdi-object            show object infomation in the vdi
  node-info             show sheepdog node information
  node-list             list nodes
  node-start            start collie daemon on the node
  node-stop             stop collie daemon on the node
  vm-info               show virtual machines information
  vm-list               list virtual machines
  cluster-info          show sheepdog cluster information
  cluster-format        format sheepdog
  cluster-shutdown      shutdown sheepdog
  help                  print help
==

Any comments and suggestions are appriciated.

Thanks,

Kazutaka