Make /dev/kvm optional
Make /dev/kvm optional

The daemon now creates /dev deterministically (thanks!).  However, it
expects /dev/kvm to be present.

The patch below restricts that requirement (1) to Linux-based systems,
and (2) to systems where /dev/kvm already exists.

I’m not sure about the way to handle (2).  We could special-case
/dev/kvm and create it (instead of bind-mounting it) in the chroot, so
it’s always available; however, it wouldn’t help much since most likely,
if /dev/kvm missing, then KVM support is missing.

tchajed/nix,offlinehacker/nix,ysangkok/nix,rycee/nix,rycee/nix,bjornfor/nix,dezgeg/nix,gebner/nix,garbas/nix,bennofs/nix,aucampia/nix,pikajude/nix,ehmry/nix,dezgeg/nix,bennofs/nix,dezgeg/nix,dezgeg/nix,bennofs/nix,ehmry/nix,peti/nix,zimbatm/nix,gebner/nix,ehmry/nix,acowley/nix,peti/nix,garbas/nix,nbp/nix,vizanto/nix,zimbatm/nix,puffnfresh/nix,wmertens/nix,NixOS/nix,bennofs/nix,offlinehacker/nix,wmertens/nix,offlinehacker/nix,ysangkok/nix,vizanto/nix,shlevy/nix,layus/nix,gridaphobe/nix,layus/nix,shlevy/nix,tchajed/nix,dtzWill/nix,rycee/nix,pikajude/nix,ehmry/nix,NixOS/nix,gridaphobe/nix,layus/nix,ttuegel/nix,bjornfor/nix,garbas/nix,aucampia/nix,rowhit/nix,garbas/nix,aucampia/nix,aucampia/nix,NixOS/nix,dtzWill/nix,gridaphobe/nix,dtzWill/nix,acowley/nix,wmertens/nix,shlevy/nix,offlinehacker/nix,pikajude/nix,ttuegel/nix,puffnfresh/nix,dtzWill/nix,jcumming/nix,rowhit/nix,joelmo/nix,NixOS/nix,dtzWill/nix,rycee/nix,rowhit/nix,peti/nix,joelmo/nix,joelmo/nix,acowley/nix,ehmry/nix,jcumming/nix,NixOS/nix,acowley/nix,gridaphobe/nix,tchajed/nix,dezgeg/nix,gebner/nix,wmertens/nix,garbas/nix,bjornfor/nix,zimbatm/nix,vizanto/nix,jcumming/nix,ttuegel/nix,layus/nix,nbp/nix,jcumming/nix,shlevy/nix,nbp/nix,vcunat/nix,joelmo/nix,gebner/nix,puffnfresh/nix,peti/nix,vizanto/nix,tchajed/nix,layus/nix,zimbatm/nix,shlevy/nix,ttuegel/nix,ysangkok/nix,peti/nix,rycee/nix,ehmry/nix,bjornfor/nix,vcunat/nix,vcunat/nix,vcunat/nix,puffnfresh/nix,rowhit/nix,nbp/nix