cluster: add internal cluster.getSettings() for test

Author: alexfernandez

lib/internal/cluster/primary.js

@@ -161,6 +161,10 @@ function removeHandlesForWorker(worker) {
   });
 }
 
+cluster.getSettings = function() {
+  return { ...cluster.settings };
+};
+
 cluster.fork = function(env) {
   cluster.setupPrimary();
   const id = ++ids;