Update AMI generator

The EBS and S3 (instance-store) AMIs are now created from the same
image. HVM instance-store AMIs are also generated.

Disk image generation has been factored out into a function
(nixos/lib/make-disk-image.nix) that can be used to build other kinds
of images.

nixos/maintainers/scripts/ec2/amazon-image.nix

@@ -0,0 +1,27 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+
+  imports =
+    [ ../../../modules/installer/cd-dvd/channel.nix
+      ../../../modules/virtualisation/amazon-image.nix
+    ];
+
+  system.build.amazonImage = import ../../../lib/make-disk-image.nix {
+    inherit pkgs lib config;
+    partitioned = config.ec2.hvm;
+    diskSize = 8192;
+    configFile = pkgs.writeText "configuration.nix"
+      ''
+        {
+          imports = [ <nixpkgs/nixos/modules/virtualisation/amazon-image.nix> ];
+          ${optionalString config.ec2.hvm ''
+            ec2.hvm = true;
+          ''}
+        }
+      '';
+  };
+
+}