在LoadRunner中设置HTTP请求time-out的时间
Error -27728: Step download timeout (120 seconds) has expired when downloading non-resource(s) [MsgId: MERR-27728]
LR默认使用120秒作为每一个HTTP请求连接和接收和timeout时间，如果一个HTTP下载页面的时间超过120秒，那么就会碰到上面的错误提示。
Step Download Timeout means that the step needed to performed for the subsequent step to be performed have reached its timeout limit (default is 120 secs) in LoadRunner.
If the error occurs during the generation of the script (replay in Vugen), it could mean that the application is really taking time of more than 120 secs to complete the download of the resources. You may want to configure the timing to suit your application needs.
如果错误是在Vugen回放脚本时发生的，也就意味着应用程序真的需要超过120秒来完成资源的下载，这时可能就需要配置run-time settings中的timeout时间了：
Increase the run-time timeout settings: In VuGen or the Controller, select Run-Time Settings > Internet Protocol: Preferences, click the Options button, and increase the "HTTP-request connect timeout" or "HTTP-request receive" timeout values.
If the error occurs during a scenario execution and happens in the middle of the scenario (usually with a large amount of load), the application is handling a lot of load and unable to attend to all the vuserrequest, thus (maybe) taking more than the configured download timing. For this,it will be better advisable to look at the system utilization of the server to seeth out any performance problems.
如果错误是在场景执行的过程中发生的，则通常是由于系统受到很大的压力而不能及时地处理某些虚拟用户的请求导致的，这应该是性能问题，需要进一步查找性能瓶颈了。
参考：
关于是否要配置timeout可参考：
http://www.loadrunnertnt.com/concepts/should-i-configure-step-download-timeout/
