title: asyncio: loop.run_until_complete(loop.create_task(f)) prints "Task exception was never retrieved" even though it clearly was propagated
body: <p>For some reason this program prints the following warning:</p>
  
  <pre><code>Task exception was never retrieved
  future: &lt;Task finished coro=&lt;coro() done, defined at /usr/lib64/python3.4/asyncio/coroutines.py:139&gt; exception=SystemExit(2,)&gt;
  </code></pre>
  
  <p>even though the exception is clearly retrieved and propagated, as <code>caught SystemExit!</code> is printed to the terminal, and process status code becomes 2.</p>
  
  <p>The same thing happens with Python 2 and trollius.</p>
  
  <p>Am I missing something?</p>
  
  <pre><code>#!/usr/bin/env python3
  
  import asyncio
  
  @asyncio.coroutine
  def comain():
      raise SystemExit(2)
  
  def main():
      loop = asyncio.get_event_loop()
      task = loop.create_task(comain())
      try:
          loop.run_until_complete(task)
      except SystemExit:
          print("caught SystemExit!")
          raise
      finally:
          loop.close()
  
  if __name__ == "__main__":
      main()
  </code></pre>