Add toplevel module, and enable modules in config

lib/k8s.nix

@@ -204,6 +204,7 @@ let
 
 in {
   options.cluster.k8s = {
+    enable = mkEnableOption "Enable kubernetes";
     nodes = mkOption {
       type = types.listOf types.attrs;
       default = [];
@@ -211,12 +212,12 @@ in {
 
     fileserver = mkOption {
       type = types.str;
-      default = "127.0.0.1";
+      default = null;
     };
 
     cidr = mkOption {
       type = types.str;
-      default = "10.11.0.0/16";
+      default = "10.0.0.0/16";
     };
 
     master = {
@@ -270,10 +271,12 @@ in {
     };
   };
 
-  config = mkMerge [
-    (mkIf cfg.k8s.master.enable kubeMaster)
-    (mkIf cfg.k8s.node.enable kubeNode)
-  ];
+  config = mkIf cfg.k8s.enable (
+    mkMerge [
+      (mkIf cfg.k8s.master.enable kubeMaster)
+      (mkIf cfg.k8s.node.enable kubeNode)
+    ]
+  );
 
   imports = [ ./os.nix ];
 }