HDFS-10336. TestBalancer failing intermittently because of not reseting UserGroupInformation completely. Contributed by Yiqun Lin.

(cherry picked from commit 932aed64d7)

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/balancer/TestBalancer.java

@@ -1870,6 +1870,7 @@ public class TestBalancer {
       });
     } finally {
       // Reset UGI so that other tests are not affected.
+      UserGroupInformation.reset();
       UserGroupInformation.setConfiguration(new Configuration());
     }
   }