treewide: use auto diskSize for make-disk-image

nixos/maintainers/scripts/cloudstack/cloudstack-image.nix

@@ -10,7 +10,6 @@ with lib;
 
   system.build.cloudstackImage = import ../../../lib/make-disk-image.nix {
     inherit lib config pkgs;
-    diskSize = 8192;
     format = "qcow2";
     configFile = pkgs.writeText "configuration.nix"
       ''

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

@@ -40,8 +40,9 @@ in {
     };
 
     sizeMB = mkOption {
-      type = types.int;
-      default = if config.ec2.hvm then 2048 else 8192;
+      type = with types; either (enum [ "auto" ]) int;
+      default = "auto";
+      example = 8192;
       description = "The size in MB of the image";
     };
 

nixos/maintainers/scripts/openstack/openstack-image.nix

@@ -12,8 +12,8 @@ with lib;
 
   system.build.openstackImage = import ../../../lib/make-disk-image.nix {
     inherit lib config;
+    additionalSpace = "1024M";
     pkgs = import ../../../.. { inherit (pkgs) system; }; # ensure we use the regular qemu-kvm package
-    diskSize = 8192;
     format = "qcow2";
     configFile = pkgs.writeText "configuration.nix"
       ''