Use a separate interface for JGroups sockets

Our standard configs currently use the "public" interface for the JGroups sockets. However, best practice is to put intra-cluster traffic on a separate network from the network handling end user requests, both for possible performance reasons and to reduce the risk of exposing clustering to unwanted, possibly malevolent, traffic.

Since that is best practice, our standard configs should reflect that. So we'll create a new 'private' interface to go along with the existing 'public', 'management', and 'unsecure' ones, and use it for the JGroups sockets.

The default address will be ${jboss.bind.address.private:127.0.0.1} consistent with the others.

Users using our standard configs who wish to use -b startup switches to control the network address will need to add -bprivate=<theaddress> to the startup command. Simply using -b=<theaddress> will no longer affect the JGroups traffic if our standard configs are used.