probe: invoke operations

Needed for diagnosis.

Add the ability to invoke simple operations via probe.sh (on all reachable instances). This is faster than having to start jconsole, finding the right member and invoking the op.

Syntax: probe.sh op=STABLE.runMessageGarbageCollection arg1 arg2 ... argN

This will find protocol STABLE and invoke operation runMessageGarbageCollection with the args given. Method matching is done on a simple argument length to parameter length comparison, and Method.invoke() is used to cast arguments (which are strings) to the parameter types.

Possible return values are sent in the hashmap, key: "STABLE.runMessagegarbageCollection", value: return value, as string