JGroupsTransport should only send messages to nodes in the cluster view

JGroupsTransport only waits for responses from nodes in the JGroups cluster view, but it still sends messages to all the nodes specified as a target. The idea was to optimize the common case by avoiding a HashSet.contains() call.

However, when a node is not in the view, messages to it still pass through the entire JGroups stack, and UNICAST3 keeps those messages in a send table for a long time (UNICAST3.conn_expiry_timeout, changed with ISPN-9038 from 0 (unlimited) to 2 minutes (JGroups default)). Having a potentially unlimited number of messages of non-members, each with its own send table, makes it much harder to estimate memory usage.