title: spring-kafka listener shutdown
body: <p>I'm trying to verify that kafka-listeners are closed gracefully when i shutdown my application (either gracefully or in some aggressive way). Can somebody point me to place where it is handled? I was looking at <code>destroy</code> and <code>close</code> methods but I couldn't locate where kafka client deregistration is actually happening.</p>
  
  <p>What happens if deregistration takes too much time? Or if some other spring bean shutdown hook takes too much time? </p>
  
  <p>Also what it actually means for currently processing events? Can they commit offset during shutdown if they happen to finish their work?</p>
  
  <p>I'm working with spring-kafka 1.3.5 version.</p>