Improve network connectivity check

[SB97]

I had TNUC autostart while having no internet connection and got this and also there is no User named Samuel on my System.

[ElPumpo]

Hi. There is already a internet connection test at the beginning, but it needs improvement. It does not catch every case of connectivity problem.

As for the marked code in red, ignore it. It is just from the build code. There is no hardcoded paths