Use xorriso instead of genisoimage, by backporting (most of) lb_binary_iso...

Use xorriso instead of genisoimage, by backporting (most of) lb_binary_iso from live-build 5.x at commit 3c303e7f.

Note that we don't import the latest version, that introduces more
changes we won't focus on right now (multi-bootloaders and EFI support).