Disable broker message forwarding by default

Still finding it to not be foolproof enough to enable generally for all
nodes in a cluster.  Specific/advanced use-cases may still consider
enabling, possibly just for specific nodes.

testing/btest/scripts/base/frameworks/cluster/forwarding.bro

@@ -28,6 +28,8 @@ global peer_count = 0;
 global peers_lost = 0;
 global fully_connected_nodes = 0;
 
+redef Broker::forward_messages = T;
+
 event forwarded_event()
 	{
 	print "got forwarded event";