fix checkstyle

Author: huangzhaobo99

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

@@ -28,7 +28,6 @@
 
 import java.io.IOException;
 import java.lang.management.ManagementFactory;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -46,22 +45,16 @@
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
 import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
-import org.apache.hadoop.hdfs.protocol.HdfsConstants;
-import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeDescriptor;
 import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeManager;
-import org.apache.hadoop.hdfs.server.blockmanagement.SlowPeerTracker;
 import org.apache.hadoop.hdfs.server.datanode.DataNode;
 import org.apache.hadoop.hdfs.server.protocol.OutlierMetrics;
 import org.apache.hadoop.metrics2.impl.ConfigBuilder;
 import org.apache.hadoop.metrics2.impl.TestMetricsConfig;
 import org.apache.hadoop.test.GenericTestUtils;
-
-import org.junit.Assert;
 import org.junit.Test;
 import org.eclipse.jetty.util.ajax.JSON;