Ensure that Hadoop is using imple authentication during impersonation…

… tests.

Some undetermined OS or library change in the GitHub Action Runner image version
has resulted in errors matching the below for tests that extend BaseTestImpersonation.

`java.io.IOException: Running in secure mode, but config doesn't have a keytab`

One guess is that the new Runner image bundles a Kerberos keytab, or other file
that is detected by Hadoop and makes it decide that it should run in Secure Mode.
This commit explicitly sets Hadoop's authentication mode simple in for Drill's
impersonation tests.

exec/java-exec/src/test/java/org/apache/drill/exec/impersonation/BaseTestImpersonation.java

@@ -103,6 +103,7 @@ protected static void startMiniDfsCluster(String testClass, boolean isImpersonat
       // Set the proxyuser settings so that the user who is running the Drillbits/MiniDfs can impersonate other users.
       dfsConf.set(String.format("hadoop.proxyuser.%s.hosts", processUser), "*");
       dfsConf.set(String.format("hadoop.proxyuser.%s.groups", processUser), "*");
+      dfsConf.set("hadoop.security.authentication", "simple");
     }
 
     // Start the MiniDfs cluster