GUI to test whether cluster nodes find each other ok

• New DiscoveryServer (GUI) which listens on a TCP socket at a given port
• Then the nodes are started and connect to the DiscoveryServer via TCP
• Connected nodes are shown in a listbox in the DiscoveryServer's GUI
• The TCP connection between a node and the DS is the control channel, and is independent of JGroups (doesn't use a JGroups config)
• The control channel is used to (a) register nodes and (b) send new JGroups configurations from the DS to the nodes
• The GUI has 4 tabs: UDP, TCP dynamic (TCP:MPING config), TCP static (TCP:TCPPING) and External discovery (TCP:TCPGOSSIP).
• Each tab has configuration specific options, e.g. for UDP we have
• multicast address
• multicast port
• TTL
• checkbox: use flush or not
• checkbox: use state transfer or not
• etc etc etc
  There are 2 actions buttons: "Discover" and "Save config". The latter saves the current configuration to a file (XML format). The "Discovery" button sends the current config to all nodes, via the control channel. Each node then creates a channel with the received config and connects to the cluster. The DiscoveryServer GUI (which also joins the same cluster) shows all nodes in a second listbox. When the number of nodes in the first and second listbox is the same, then this shows that the config works. In that case, the user can press "Save config" and use the generated config with all cluster nodes.
• In case UDP doesn't work or a user wants a TCP based config from the onset, the user simply clicks on the TCP tab, fills in the required information and clicks on "Discover".
• The initial config for each tab is provided by the corresponding default shipped with JGroups, e.g. UDP uses udp.xml

In a second stage, we could also not just verify that the cluster can be established, but also run some perf tests over it.