nixos.tests.installer: Fix test failures due to network being disabled

nixos/modules/security/sudo.nix

@@ -83,7 +83,7 @@ in
 	  {src = pkgs.writeText "sudoers-in" cfg.configFile; }
           # Make sure that the sudoers file is syntactically valid.
           # (currently disabled - NIXOS-66)
-          "${pkgs.sudo.override {keepVisudo = true;}}/sbin/visudo -f $src -c &&
+          "${pkgs.sudoWithVisudo}/sbin/visudo -f $src -c &&
 	      cp $src $out";
         target = "sudoers";
         mode = "0440";

nixos/tests/installer.nix

@@ -22,6 +22,7 @@ let
             isoImage.storeContents =
               [ pkgs.glibcLocales
                 pkgs.sudo
+                pkgs.sudoWithVisudo
                 pkgs.docbook5
                 pkgs.docbook5_xsl
                 pkgs.grub

pkgs/top-level/all-packages.nix

@@ -2080,6 +2080,8 @@ let
 
   sudo = callPackage ../tools/security/sudo { };
 
+  sudoWithVisudo = sudo.override { keepVisudo = true; };
+
   suidChroot = builderDefsPackage (import ../tools/system/suid-chroot) { };
 
   super = callPackage ../tools/security/super { };