Make the minimal iso not use profile/minimal, +vim

The profile minimal has several drawbacks: no man pages, unusual 'dbus'
lib that makes many X11 pieces to rebuild, etc.

With xz compression in the squashfs, despite these additions, the iso is
smaller than what it was in 16.09.

nixos/modules/installer/cd-dvd/installation-cd-minimal.nix

@@ -1,11 +1,15 @@
 # This module defines a small NixOS installation CD.  It does not
 # contain any graphical stuff.
 
-{ config, lib, ... }:
+{ config, lib, pkgs, ... }:
 
 {
   imports =
     [ ./installation-cd-base.nix
-      ../../profiles/minimal.nix
+    ];
+
+  environment.systemPackages =
+    [
+      pkgs.vim
     ];
 }