HDFS-15345. RouterPermissionChecker#checkSuperuserPrivilege should use UGI#getGroups after HADOOP-13442.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterPermissionChecker.java

@@ -126,7 +126,7 @@ public class RouterPermissionChecker extends FSPermissionChecker {
     }
 
     // Is the user a member of the super group?
-    List<String> groups = Arrays.asList(ugi.getGroupNames());
+    List<String> groups = ugi.getGroups();
     if (groups.contains(superGroup)) {
       return;
     }