Decouple machine configuration and deployment

This allows custom scripts to access machine-specific variables.

deploy.nix

@@ -45,7 +45,7 @@ let
     in
     kropsPkgs.krops.writeDeploy "deploy-${hostname}" {
       source = source;
-      target = lib.mkTarget (if target == null then "root@${hostname}" else target) // {
+      target = lib.mkTarget target // {
         extraOptions = [
           # force allocation of tty to allow aborting with ^C and to show build progress
           "-t"
@@ -53,8 +53,6 @@ let
       };
     };
 in
-builtins.mapAttrs (hostname: configuration: kropsDeploy ({ inherit hostname; } // configuration))
-{
-  nunotaba = { };
-  sayuri = { };
-}
+builtins.mapAttrs
+  (hostname: configuration: kropsDeploy ({ inherit hostname; } // configuration))
+  (import ./machines)

machines/default.nix

@@ -0,0 +1,18 @@
+let
+  sources = import ../nix/sources.nix;
+
+  pkgs = import sources.nixpkgs { };
+  lib = pkgs.lib;
+in
+lib.mapAttrs
+  (hostname: options: {
+    inherit hostname;
+    target =
+      if lib.hasAttr "target" options
+      then options.target
+      else "root@${hostname}";
+  })
+{
+  nunotaba = { };
+  sayuri = { };
+}