StateTransferFunctionalTest random failures

Since the ISPN-6214 fix, the global components are started when the DefaultCacheManager is started. This includes LocalTopologyManager and ClusterTopologyManager, created in the GlobalComponentRegistry constructor, and they also pull in the Transport component.

In StateTransferFunctionalTest and its subclasses, this means the JGroups channel is created and joins the cluster before the JoiningNode registers its view listener. Because the listener is registered after the view update, it doesn't receive any notifications, and waitForJoin() always times out.

We should remove the JoiningNode class altogether, because merges during initial cluster formation are practically impossible with our current test setup.