[ISSUE #2170] Update BrokerOuterAPI (#2203)

* READM.md: update BrokerOuterAPI

* fix tab error

* use thread-safe list

* use thread-safe list

broker/src/main/java/org/apache/rocketmq/broker/out/BrokerOuterAPI.java

@@ -16,10 +16,10 @@
  */
 package org.apache.rocketmq.broker.out;
 
-import com.google.common.collect.Lists;
 import java.io.UnsupportedEncodingException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Vector;
 import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
@@ -123,7 +123,7 @@ public class BrokerOuterAPI {
         final int timeoutMills,
         final boolean compressed) {
 
-        final List<RegisterBrokerResult> registerBrokerResultList = Lists.newArrayList();
+        final List<RegisterBrokerResult> registerBrokerResultList = new Vector<>();
         List<String> nameServerAddressList = this.remotingClient.getNameServerAddressList();
         if (nameServerAddressList != null && nameServerAddressList.size() > 0) {