svn merge -c 1595978 merging from trunk to branch-2 to fix:HDFS-6397. NN shows inconsistent value in deadnode count. Contributed by Mohammad Kamrul Islam. Fixing merge error

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1595984 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestHostsFiles.java

@@ -19,6 +19,7 @@ package org.apache.hadoop.hdfs.server.namenode;
 
 import static org.junit.Assert.assertTrue;
 
+import java.lang.management.ManagementFactory;
 import java.net.InetSocketAddress;
 import java.net.URL;
 
@@ -36,6 +37,9 @@ import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.junit.Test;
 
+import javax.management.MBeanServer;
+import javax.management.ObjectName;
+
 /**
  * DFS_HOSTS and DFS_HOSTS_EXCLUDE tests
  *