Add timeout to prevent test hanging in testDisconnectWhenConnectionBreak

The test was hanging because testThread.join() was waiting indefinitely.
If disconnect() hangs when ZK connection is broken, the test would wait
forever. This caused the CI test to timeout after 15 minutes.

Fix by:
1. Add 10 second timeout to join() to prevent indefinite wait
2. Make forceful stop conditional - only if thread is still alive
3. Add descriptive assertion message

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: junkaixue

helix-core/src/test/java/org/apache/helix/integration/TestZkConnectionLost.java

@@ -132,13 +132,17 @@ public void run() {
     };
     try {
       testThread.start();
-      testThread.join();
-      Assert.assertTrue(disconnected.get());
+      // Add timeout to prevent test from hanging forever if disconnect() hangs
+      testThread.join(10000);
+      Assert.assertTrue(disconnected.get(),
+          "disconnect() should complete within 10 seconds");
       Assert.assertFalse(controllerManager.isConnected());
     } finally {
-      testThread.stop();
-      TestHelper.verify(() -> testThread.getState().equals(Thread.State.TERMINATED),
-          TestHelper.WAIT_DURATION);
+      if (testThread.isAlive()) {
+        testThread.stop();
+        TestHelper.verify(() -> testThread.getState().equals(Thread.State.TERMINATED),
+            TestHelper.WAIT_DURATION);
+      }
       _zkServerRef.set(TestHelper.startZkServer(_zkAddr, null, false));
     }
   }