Add switch to avoid throttling traffic on localhost or specific port

[soulgalore]

When you use Browsertime and Throttle on a Mac and use Firefox it fails if you set a slow connection, the reason is that throttle also slow down the traffic between Geckodriver and Firefox see https://github.com/mozilla/geckodriver/issues/1903

Using Chrome it works but Chrome is slow and I guess it's the same problem there, we slow down the traffic between Chromedriver and Chrome.