Major Description
The following code leaks a producer network thread:
ks = new KafkaStreams(...);
ks.close();
The underlying issue is that KafkaStreams creates a bunch of StreamsThreads via StreamThread.create, which in turn creates a bunch of stuff (including a producer). These resources are cleaned up only when the thread exits. So if the thread was never started, then they are never cleaned up. StreamThread.shutdown should clean up if it sees that the thread has never been started.
