nixos: add preferLocalBuild=true; on derivations for config files

nixos/modules/services/logging/logcheck.nix

@@ -5,7 +5,7 @@ with lib;
 let
   cfg = config.services.logcheck;
 
-  defaultRules = pkgs.runCommand "logcheck-default-rules" {} ''
+  defaultRules = pkgs.runCommand "logcheck-default-rules" { preferLocalBuild = true; } ''
                    cp -prd ${pkgs.logcheck}/etc/logcheck $out
                    chmod u+w $out
                    rm -r $out/logcheck.*

nixos/modules/services/logging/logstash.nix

@@ -27,7 +27,10 @@ let
 
   logstashSettingsYml = pkgs.writeText "logstash.yml" cfg.extraSettings;
 
-  logstashSettingsDir = pkgs.runCommand "logstash-settings" {inherit logstashSettingsYml;} ''
+  logstashSettingsDir = pkgs.runCommand "logstash-settings" {
+      inherit logstashSettingsYml;
+      preferLocalBuild = true;
+    } ''
     mkdir -p $out
     ln -s $logstashSettingsYml $out/logstash.yml
   '';