Bug#861380: 861380 Workaround for black screen upon installer boot
If one disables the dedicated NVIDIA GPU in the system's BIOS, the
Stretch installer boots correctly and installation succeeds without
However, once the installed system boots, it hangs. This can be fixed by
activating hybrid graphics in the BIOS again.
So for installation: Disallow hybrid graphics.
For booting the installed system: Enable hybrid graphics.