nixos/testing: Don't shadow "lib" in makePerlPath.

Regression introduced by 032f0ffdd0.

The change doesn't look obvious at the first sight why it may cause
problems with lib.makePerlPath, but it introduces a Perl package called
"lib".

And using "with perlPackages;" uses the Perl library "lib" instead of
the lib attribute set from pkgs.

So let's use pkgs.lib.makePerlPath directly in hope that there won't be
a Perl package anytime soon which is called "pkgs".

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nixos/lib/testing.nix

@@ -28,7 +28,7 @@ rec {
 
         wrapProgram $out/bin/nixos-test-driver \
           --prefix PATH : "${qemu_kvm}/bin:${vde2}/bin:${netpbm}/bin:${coreutils}/bin" \
-          --prefix PERL5LIB : "${with perlPackages; lib.makePerlPath [ TermReadLineGnu XMLWriter IOTty FileSlurp ]}:$out/lib/perl5/site_perl"
+          --prefix PERL5LIB : "${with perlPackages; pkgs.lib.makePerlPath [ TermReadLineGnu XMLWriter IOTty FileSlurp ]}:$out/lib/perl5/site_perl"
       '';
   };