nixos/testing: Add pkgs parameter

This parameter is for packages to use in VMs, unlike hostPkgs.

nixos/lib/testing-python.nix

···
     ./testing/name.nix
     ./testing/network.nix
     ./testing/nodes.nix
+    ./testing/pkgs.nix
     ./testing/run.nix
     ./testing/testScript.nix
     {

nixos/lib/testing/pkgs.nix

···
+{ config, lib, hostPkgs, ... }:
+{
+  config = {
+    # default pkgs for use in VMs
+    _module.args.pkgs = hostPkgs;
+
+    defaults = {
+      # TODO: a module to set a shared pkgs, if options.nixpkgs.* is untouched by user (highestPrio) */
+    };
+  };
+}

nixos/tests/3proxy.nix

···
-import ./make-test-python.nix ({ pkgs, ...} : {
+{ lib, pkgs, ... }: {
   name = "3proxy";
   meta = with pkgs.lib.maintainers; {
     maintainers = [ misuzu ];
···
         "${pkgs.wget}/bin/wget -e use_proxy=yes -e http_proxy=http://192.168.0.4:3128 -S -O /dev/null http://127.0.0.1:9999"
     )
   '';
-})
+}

nixos/tests/all-tests.nix

···
     ;
 
 in {
-  _3proxy = handleTest ./3proxy.nix {};
+  _3proxy = runTest ./3proxy.nix;
   acme = handleTest ./acme.nix {};
   adguardhome = handleTest ./adguardhome.nix {};
   aesmd = handleTest ./aesmd.nix {};