LuaMinXmlHttpRequest can not get error message if failed to connect network

[minggo]

[samuele3hu]

When LuaMinXmlHttpRequest fails to connect network, it would output the log in the console as follow:
cocos2d: Response failed, error buffer: Connection timed out after 30132 milliseconds

[samuele3hu]

Add callback when connect network,the related pr is at #8868