Extend wait time to 20s in SecurityIntegTest

This kind of sucks, because we shouldn't have to wait that long for tests to run.
But they're failing CI with some regularity, and we rely on these integration tests.

Original commit: elastic/x-pack-elasticsearch@3f4acb2a32

plugin/src/test/java/org/elasticsearch/test/SecurityIntegTestCase.java

@@ -49,6 +49,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -484,7 +485,7 @@ public abstract class SecurityIntegTestCase extends ESIntegTestCase {
                         assertTrue(indexRoutingTable.allPrimaryShardsActive());
                     }
                 }
-            });
+            }, 20, TimeUnit.SECONDS);
         }
     }