ocfs2: live heartbeat depends on the local node configuration

Removing the local node configuration out from underneath a running
heartbeat is "bad".  Provide an API in the ocfs2 nodemanager to request
a configfs dependancy on the local node, then use it in heartbeat.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>