Test: don't use setDaemon in DiscoveryWithServiceDisruptionsIT.

core/src/test/java/org/elasticsearch/discovery/DiscoveryWithServiceDisruptionsIT.java

@@ -476,7 +476,6 @@ public class DiscoveryWithServiceDisruptionsIT extends ESIntegTestCase {
                 });
 
                 thread.setName(name);
-                thread.setDaemon(true);
                 thread.start();
                 indexers.add(thread);
             }