ocfs2: add DLM recovery callbacks

ocfs2: add DLM recovery callbacks

These are the callbacks called by the fs/dlm code in case the membership
changes.  If there is a failure while/during calling any of these, the DLM
creates a new membership and relays to the rest of the nodes.

recover_prep() is called when DLM understands a node is down.
recover_slot() is called once all nodes have acknowledged recover_prep and
recovery can begin.  recover_done() is called once the recovery is
complete.  It returns the new membership.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>