Fix GCE image build.

(cherry picked from commit 98af87cd4abb0cd77e8a51cfdf6913a92d088784)

nixos/modules/virtualisation/google-compute-image.nix

@@ -63,11 +63,12 @@ in
 
           # Register the paths in the Nix database.
           printRegistration=1 perl ${pkgs.pathsFromGraph} /tmp/xchg/closure | \
-              chroot /mnt ${config.nix.package}/bin/nix-store --load-db
+              chroot /mnt ${config.nix.package}/bin/nix-store --load-db --option build-users-group ""
 
           # Create the system profile to allow nixos-rebuild to work.
           chroot /mnt ${config.nix.package}/bin/nix-env \
-              -p /nix/var/nix/profiles/system --set ${config.system.build.toplevel}
+              -p /nix/var/nix/profiles/system --set ${config.system.build.toplevel} \
+              --option build-users-group ""
 
           # `nixos-rebuild' requires an /etc/NIXOS.
           mkdir -p /mnt/etc