ViewDFS#getDelegationToken should not throw UnsupportedOperationException.

When starting Hive in secure environment, it is throwing UnsupportedOprationException from ViewDFS.

at org.apache.hive.service.server.HiveServer2.start(HiveServer2.java:736) ~[hive-service-3.1.3000.7.2.3.0-54.jar:3.1.3000.7.2.3.0-54]
at org.apache.hive.service.server.HiveServer2.startHiveServer2(HiveServer2.java:1077) ~[hive-service-3.1.3000.7.2.3.0-54.jar:3.1.3000.7.2.3.0-54]
... 9 more
Caused by: java.lang.UnsupportedOperationException
at org.apache.hadoop.hdfs.ViewDistributedFileSystem.getDelegationToken(ViewDistributedFileSystem.java:1042) ~[hadoop-hdfs-client-3.1.1.7.2.3.0-54.jar:?]
at org.apache.hadoop.security.token.DelegationTokenIssuer.collectDelegationTokens(DelegationTokenIssuer.java:95) ~[hadoop-common-3.1.1.7.2.3.0-54.jar:?]
at org.apache.hadoop.security.token.DelegationTokenIssuer.addDelegationTokens(DelegationTokenIssuer.java:76) ~[hadoop-common-3.1.1.7.2.3.0-54.jar:?]
at org.apache.tez.common.security.TokenCache.obtainTokensForFileSystemsInternal(TokenCache.java:140) ~[tez-api-0.9.1.7.2.3.0-54.jar:0.9.1.7.2.3.0-54]
at org.apache.tez.common.security.TokenCache.obtainTokensForFileSystemsInternal(TokenCache.java:101) ~[tez-api-0.9.1.7.2.3.0-54.jar:0.9.1.7.2.3.0-54]
at org.apache.tez.common.security.TokenCache.obtainTokensForFileSystems(TokenCache.java:77) ~[tez-api-0.9.1.7.2.3.0-54.jar:0.9.1.7.2.3.0-54]
at org.apache.hadoop.hive.ql.exec.tez.TezSessionState.createLlapCredentials(TezSessionState.java:443) ~[hive-exec-3.1.3000.7.2.3.0-54.jar:3.1.3000.7.2.3.0-54]
at org.apache.hadoop.hive.ql.exec.tez.TezSessionState.openInternal(TezSessionState.java:354) ~[hive-exec-3.1.3000.7.2.3.0-54.jar:3.1.3000.7.2.3.0-54]
at org.apache.hadoop.hive.ql.exec.tez.TezSessionState.open(TezSessionState.java:313) ~[hive-exec-3.1.3000.7.2.3.0-54.jar:3.1.3000.7.2.3.0-54]