Scala gRPC doesn't exit if it can't bind to the specified port

[arosien]

For example, if the C++ server isn't killed in build.sh before the Scala gRPC tests start.

Exception in thread "main" akka.stream.impl.io.ConnectionSourceStage$$anon$1$$anon$2: Bind failed because of java.net.BindException: [/127.0.0.1:9000] Address already in use
Caused by: java.net.BindException: [/127.0.0.1:9000] Address already in use
	at java.base/sun.nio.ch.Net.bind0(Native Method)
	at java.base/sun.nio.ch.Net.bind(Net.java:455)
	at java.base/sun.nio.ch.Net.bind(Net.java:447)
	at java.base/sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:227)
	at java.base/sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:80)
	at akka.io.TcpListener.liftedTree1$1(TcpListener.scala:60)
	at akka.io.TcpListener.<init>(TcpListener.scala:57)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
	at akka.util.Reflect$.instantiate(Reflect.scala:73)
	at akka.actor.ArgsReflectConstructor.produce(IndirectActorProducer.scala:101)
	at akka.actor.Props.newActor(Props.scala:226)
	at akka.actor.ActorCell.newActor(ActorCell.scala:613)
	at akka.actor.ActorCell.create(ActorCell.scala:640)
	at akka.actor.ActorCell.invokeAll$1(ActorCell.scala:513)
	at akka.actor.ActorCell.systemInvoke(ActorCell.scala:535)
	at akka.dispatch.Mailbox.processAllSystemMessages(Mailbox.scala:295)
	at akka.dispatch.Mailbox.run(Mailbox.scala:230)
	at akka.dispatch.Mailbox.exec(Mailbox.scala:243)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)