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>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>