Test: override beforeIndexDeletion for audit trail tests

The beforeIndexDeletion method expects that nothing is still indexing when it runs
but this is not the case as the index audit trail will continue indexing events that
occur as checks are being performed in the cluster.

Original commit: elastic/x-pack-elasticsearch@02001a5222

src/test/java/org/elasticsearch/shield/audit/index/IndexAuditTrailEnabledTests.java

@@ -34,6 +34,13 @@ public class IndexAuditTrailEnabledTests extends ShieldIntegrationTest {
         return builder.build();
     }
 
+    @Override
+    public void beforeIndexDeletion() {
+        // For this test, this is a NO-OP because the index audit trail will continue to capture events and index after
+        // the tests have completed. The default implementation of this method expects that nothing is performing operations
+        // after the test has completed
+    }
+
     @Test
     public void testIndexAuditTrailIndexExists() throws Exception {
         awaitIndexCreation();