Optimize the test_ip function in the request_tester.lua file

[houjq3]

[alexazhou]

I'am very thank you for your work, but i can't merage this pull request currently.

This commit can handle some condition but may cause risk some times. Like user can modify there header to bypass filter.

I think i need to add some config , let user can choose if they would like to use ip address in the header.

After that i would like to merage the PR

[JoyChou93]

This code is best to customize.