Backend connection cannot be established when network band-width is limited

[actiontech-bot]

Raised by: helingyun Steps:

1. set limit on network band-width by TC
2. Found errors in Dble logs:

2017-05-22 14:51:25.105  WARN [Timer0] (io.mycat.backend.mysql.nio.handler.SingleNodeHandler.backConnectionErr(SingleNodeHandler.j
ava:182)) - execute  sql err : errno:1023 sql timeout con:MySQLConnection [id=4241, lastTime=1495435854444, user=action, schema=te
st_hly_2, old shema=test_hly_2, borrowed=true, fromSlaveDB=false, threadId=5372, charset=latin1, txIsolation=3, autocommit=true, a
ttachment=dn1{select my_name,my_idcard,my_phone from user_info WHERE id in (98423114,98423124)}.0, respHandler=SingleNodeHandler [
node=dn1{select my_name,my_idcard,my_phone from user_info WHERE id in (98423114,98423124)}.0, packetId=1], host=10.186.17.101, por
t=3309, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] frontend host:10.186.17.108/33264/action
2017-05-22 14:51:42.082 ERROR [$_NIOConnector] (io.mycat.net.NIOConnector.finishConnect(NIOConnector.java:127)) - error:
java.net.ConnectException: Connection timed out
        at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[?:1.8.0_121]
        at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717) ~[?:1.8.0_121]
        at io.mycat.net.NIOConnector.finishConnect(NIOConnector.java:137) ~[Action_Mycat-2.17.04.0.jar:?]
        at io.mycat.net.NIOConnector.finishConnect(NIOConnector.java:115) [Action_Mycat-2.17.04.0.jar:?]
        at io.mycat.net.NIOConnector.run(NIOConnector.java:83) [Action_Mycat-2.17.04.0.jar:?]

3. Backend connections failed, but logs are not clear enough.