fix producer Stop() EOF

[mengskysama]

when producer.Stop() EOF exception occur

2016/12/01 09:44:47 ERR  3856 (10.160.3.70:4150) IO error - EOF
2016/12/01 09:44:47 INF  3856 (10.160.3.70:4150) beginning close
2016/12/01 09:44:47 INF  3856 (10.160.3.70:4150) readLoop exiting
2016/12/01 09:44:47 INF  3856 (10.160.3.70:4150) breaking out of writeLoop
2016/12/01 09:44:47 INF  3856 (10.160.3.70:4150) writeLoop exiting
2016/12/01 09:44:47 INF  3856 stopping
2016/12/01 09:44:47 INF  3856 exiting router

[judwhite]

@mreiferson @jehiah Should it check c.closeFlag if the error does contain "use of closed network connection"? Otherwise, it might skip a call to c.delegate.OnIOError which delegates to (p *Producer) close(). It's not immediately obviously what conditions inside the net package can lead to net.errClosing.

[mreiferson]

My assumption is that there's an edge case where you're cleanly shutting down but you don't "use a closed connection" but instead hit an "expected" EOF.

This person was clearly getting a log message despite the existing logic, which I think confirms that.