HDFS-10346: add org.apache.hadoop.util.StringUtils import.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java

@@ -66,6 +66,7 @@ import org.apache.hadoop.security.authentication.util.KerberosUtil;
 import org.apache.hadoop.security.token.Token;
 import org.apache.hadoop.security.token.TokenIdentifier;
 import org.apache.hadoop.util.Shell;
+import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.util.Time;
 
 import com.google.common.annotations.VisibleForTesting;