Use hut-substituter module in owl{1,2} and raccoon

m/module/hut-substituter.nix

@@ -1,10 +1,9 @@
 { config, ... }:
+  # Don't add hut as a cache to itself
+  assert config.networking.hostName  != "hut";
 {
-  nix.settings =
-    # Don't add hut as a cache to itself
-    assert config.networking.hostName != "hut";
-    {
-      substituters = [ "https://jungle.bsc.es/cache" ];
-      trusted-public-keys = [ "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" ];
-    };
+  nix.settings = {
+    substituters = [ "https://jungle.bsc.es/cache" ];
+    trusted-public-keys = [ "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" ];
+  };
 }