title: Shutdown spark structured streaming gracefully
body: <p>There is a way to enable graceful shutdown of spark streaming by setting property <code>spark.streaming.stopGracefullyOnShutdown</code> to true and then kill the process with <code>kill -SIGTERM</code> command. However I don't see such option available for structured streaming (SQLContext.scala). </p>
  
  <p>Is the shutdown process different in structured streaming? Or is it simply not implemented yet?</p>