diagstatus CLI should not to use JMX to obtain information from local node to avoid ConnectException on 127.0.0.1

INFRAUTILS-36 made me look more into the code in DiagStatusCommand, and I don't understand why on earth it uses JMX to call LOCAL code? I get the point of that code to get diagstatus from remote cluster members, but to query the local diagstatus, that seems... weird - we can, easily, just call the local service!

I'll raise a change proposing this.