fix the TestDFSUpgradeWithHA due to BindException

see https://builds.apache.org/job/PreCommit-HDFS-Build/9092//testReport/org.apache.hadoop.hdfs.server.namenode.ha/TestDFSUpgradeWithHA/testNfsUpgrade/ :
Error Message

Port in use: localhost:57896
Stacktrace

java.net.BindException: Port in use: localhost:57896
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:444)
at sun.nio.ch.Net.bind(Net.java:436)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:214)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
at org.mortbay.jetty.nio.SelectChannelConnector.open(SelectChannelConnector.java:216)
at org.apache.hadoop.http.HttpServer2.openListeners(HttpServer2.java:868)
at org.apache.hadoop.http.HttpServer2.start(HttpServer2.java:809)
at org.apache.hadoop.hdfs.server.namenode.NameNodeHttpServer.start(NameNodeHttpServer.java:142)
at org.apache.hadoop.hdfs.server.namenode.NameNode.startHttpServer(NameNode.java:704)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:591)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:763)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:747)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1443)
at org.apache.hadoop.hdfs.MiniDFSCluster.restartNameNode(MiniDFSCluster.java:1815)
at org.apache.hadoop.hdfs.MiniDFSCluster.restartNameNode(MiniDFSCluster.java:1796)
at org.apache.hadoop.hdfs.server.namenode.ha.TestDFSUpgradeWithHA.testNfsUpgrade(TestDFSUpgradeWithHA.java:285)