shutdown the pool now to avoid delayed shutdownchannelgroupexception

[weiyu2001]

This is to fix the mvn -q test -DclassName=TestAsyncTcpTransport run failure with ShutdownChannelGroupException at the end

[weiyu2001]

@jefft0 those exceptions are normal behavior under abnormal network connectivity. Some are thrown/logged inside AsyncTcpTransport and the rest are caught/logged by the test code trying to send packets while server is down. It is difficult to time when the send will throw exception because of the async timing of the send and reconnect. I can ignore those exceptions caught by test and not log them or simply log one line to show test procession but there will be other exceptions logged inside AsyncTcpTransport. Or I can turn off all logging for the whole test run (sounds like cheating). You have any better idea? please advise.

[jefft0]

OK if it's what you expected. I don't have a better idea.