Probe will call into a bunch of listeners on TP, e.g. implementing
String handleProbe(String[] keys);

On the client side, probe.sh -query KEY-1 KEY2 KEY-3
would send a probe to all nodes, and all registered listeners would get a
handleProbe(KEY1, KEY-2, KEY-3) invoked.

The aggregated data is then sent back to the client, possibly in multiple packets is the size gets too big.

This allows apps to define special handling of their own keywords.