Refactoring of NetTestLoader
Refactoring of NetTestLoader

* Make it clear that calling one of those methods can be extremely dangerous
* Kill a bug spotted thanks to unittesting

juga0/ooni-probe,Karthikeyan-kkk/ooni-probe,0xPoly/ooni-probe,Karthikeyan-kkk/ooni-probe,kdmurray91/ooni-probe,lordappsec/ooni-probe,lordappsec/ooni-probe,Karthikeyan-kkk/ooni-probe,kdmurray91/ooni-probe,0xPoly/ooni-probe,kdmurray91/ooni-probe,Karthikeyan-kkk/ooni-probe,lordappsec/ooni-probe,juga0/ooni-probe,0xPoly/ooni-probe,lordappsec/ooni-probe,juga0/ooni-probe,juga0/ooni-probe,0xPoly/ooni-probe,kdmurray91/ooni-probe