Add cluster-nodes option while creating md
home-cluster while creating an array

If home-cluster is not specified, this is auto-detected using
dlopen corosync cmap library.
Use n bitmaps for clustered mode

For a cluster, bitmaps equal to number of nodes is written.
The bitmaps are also aligned to 4k as opposed to 256 previously.
Examine bitmap to show all nodes
Add a new clustered disk

A clustered disk is added by the traditional --add sequence
The other nodes, issue one of the following depending on
whether the disk was found:

--cluster-confirm Y:/dev/whatever
or
--cluster-confirm Y:missing