Defaults createTopics' param async=false

Async must default to false.
It is dangerous to use async=true for createTopics unless explicitly specified.

For running async calls, the subsequent steps (such as addTopics) will fail as the topics are yet to be created/in the progress of creation.
It is the nature of async to return immediately even before the createTopics is completed.

This fixes the regression from the fix 5fd3764.

Author: lamweili

lib/baseClient.js

@@ -253,7 +253,7 @@ Client.prototype.createTopics = function (topics, isAsync, cb) {
 
   if (typeof isAsync === 'function' && typeof cb === 'undefined') {
     cb = isAsync;
-    isAsync = true;
+    isAsync = false;
   }
 
   try {

test/test.offset.js

@@ -14,7 +14,7 @@ describe('Offset', function () {
     client = new Client();
     producer = new Producer(client);
     producer.on('ready', function () {
-      producer.createTopics(['_exist_topic_3_test'], true, function (err) {
+      producer.createTopics(['_exist_topic_3_test'], false, function (err) {
         done(err);
       });
     });

test/test.producer.js

@@ -46,7 +46,7 @@ var client, producer, noAckProducer, producerKeyed;
             producer.once('ready', callback);
           },
           function (callback) {
-            producer.createTopics([EXISTS_TOPIC_3], true, callback);
+            producer.createTopics([EXISTS_TOPIC_3], false, callback);
           }
         ],
         done