Terminate JVM of already running instances

[AhmedMagedC]

Resolves #1066

Changes

added System.exit(0)
why?
when new Processing instance opens, a client socket is instantiated and connected to the main server socket (initiated by the main instance), then the main instance handles opening the sketch
but what about the instance that created the socket in the first place? we didn't terminate it's JVM, so it remains consuming resources and doing pretty much nothing

Tests

i validate the changes by trying to locally build multiple instances
everything works as expected, and these instances automatically exits

[Stefterv]

Hi @AhmedMagedC Looks good!

Code wise, would you be up for changing the code-flow that it becomes clearer when System.exit(0) is called?
Right now I'm a bit worried that it'll be missed the next time changes are made since the check is on line 254 and the action is on line 327

[AhmedMagedC]

Done! what do you think @Stefterv?

[Stefterv]

Perfect! thank you very much