Simulator.java: shutdown if serial port open fails
Simulator.java: shutdown if serial port open fails

If we can't connect to the autopilot in HITL, we should not continue but
stop jMAVSim. Otherwise, the user won't realize that HITL is not actually
working and get confused.

PX4/jMAVSim,PX4/jMAVSim,PX4/jMAVSim