[patch 1/3] OCFS2 - Expose struct o2nm_cluster

Subsequent patches (namely userspace heartbeat and configurable timeouts)
require access to the o2nm_cluster struct.  This patch does the necessary
shuffling.

Signed-off-by: Andrew Beekhof <abeekhof@suse.de>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>