Getting HTTP status code for the last request

[kamal]

This is probably an easy fix by having the NetworkManager provide the information in the NetworkAccessManager::handleFinished callback. The issue to be aware of is Capybara only cares about the status code of the original request. When you load a page in PhantomJS, it will start loading all the other assets like images and CSS as a real browser should, so we'll need to ignore those. Even if you pass in the --load-images=no option, Socket.IO's requests will still go through the callback.