Discovery: add cluster name to discovery request to be able to discard responses from different clusters

When we have 2 groups ONE and TWO:
ONE: 228.8.8.8:7500 and
TWO: 228.1.2.3:7500

In some cases, they will receive each other's traffic (http://wiki.jboss.org/wiki/Wiki.jsp?page=PromiscuousTraffic).
Assume ONE has members

and TWO has no members yet. When D (in cluster TWO) starts up and sends out a discovery request, it might also receive discovery responses from ONE (A,B,C). D might now identify A as coordinator and send a JOIN-REQ to A. However, A will discard that request as the group name of D's request is TWO rather than ONE !
Result: D's JOIN-REQ will hang !

Note that the transport (TP) does drop messages from different clusters, but this happens only after the new member has joined the group, so discovery requests/responses from different groups are not discarded.

Tasks:

• Verify that the transport-name matching algorithm in TP is correct
• Confirm that - on initial discovery - discovery requests and responses are not matched