NTLM and responseCallback

[mstoykov]

As reported in https://github.com/loadimpact/k6/issues/1828#issuecomment-794170024 NTLM apparently might be having 2 401 responses before an actual real authentication.

Unfortunately, this wasn't reported early enough to get in v0.31.0 and also I have some doubts looking at the code and also, unfortunately, testing NTLM is ... hard or practically impossible under Linux as I can't find a ntlm server implementation that I can setup. I tried this but probably due to the age of the article I am not able to make apache actually return me 401 ... so :shrug: .

We could possibly try to use this golang implementation for server, but I would really prefer if we have some fairly standard web server with NTLM enabled that we can use for basic manual testing especially during changes like this