Well, trying many things...
like removing IOMMU in nova command line... did not help. was rebooting anyway.
I now switched from 64 build to 32 bits build, trying pistachio, and run/log. I got some text result that way: Kickstart ...
Multiboot compliant loader detected ...
Loading kernel...
(that's the last line)
I suppose this is Pistachio speaking... and that the kernel spoken about is Genode kernel?