When running as root, use build users by default
When running as root, use build users by default

This removes the need to have a nix.conf, and prevents people from
accidentally running Nix builds as root.

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