bug#22633: Provide a kvm-less qemu / guix system vm

[Christopher Allan Webber <cwebber@dustycloud.org>]

Ludovic Courtès writes:

> Libkmod honors ‘modprobe.blacklist’ (in ‘kcmdline_parse_result’ in
> libkmod-config.c) and eudev passes KMOD_PROBE_APPLY_BLACKLIST
> unconditionally in udev-builtin-kmod.c (meaning it honors it too.)
>
> However, there’s a hyphen-vs-underscore issue, I think.  Namely, the
> file is called ‘kvm-intel.ko’, but the normalized module name is
> ‘kvm_intel’, and this is what libkmod expects (commit 5c7dd5a changes
> our code to normalize module names similarly.)
>
> Could you try with “modprobe.blacklist=kvm_intel”?

I tried it, and it works!  This does mean that /dev/kvm doesn't exist,
so I should be able to write a patch to Guix that disables kvm for qemu
when /dev/kvm is absent.  Great! :)