Ensure operator can shut down quickly

Author: rjeberhard

operator/src/main/java/oracle/kubernetes/operator/BaseMain.java

@@ -1,4 +1,4 @@
-// Copyright (c) 2022, 2023, Oracle and/or its affiliates.
+// Copyright (c) 2022, 2024, Oracle and/or its affiliates.
 // Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl.
 
 package oracle.kubernetes.operator;
@@ -249,6 +249,7 @@ void waitForDeath() {
 
     acquireShutdownSignal();
 
+    wrappedExecutorService.shutdown();
     stopAllWatchers();
   }
 

operator/src/main/java/oracle/kubernetes/operator/work/Engine.java

@@ -1,4 +1,4 @@
-// Copyright (c) 2018, 2023, Oracle and/or its affiliates.
+// Copyright (c) 2018, 2024, Oracle and/or its affiliates.
 // Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl.
 
 package oracle.kubernetes.operator.work;
@@ -48,7 +48,12 @@ public Engine() {
    * @return executor service
    */
   public static ScheduledExecutorService wrappedExecutorService(Container container) {
-    ScheduledThreadPoolExecutor threadPool = new ScheduledThreadPoolExecutor(DEFAULT_THREAD_COUNT);
+    ScheduledThreadPoolExecutor threadPool = new ScheduledThreadPoolExecutor(
+        DEFAULT_THREAD_COUNT, r -> {
+          Thread t = Executors.defaultThreadFactory().newThread(r);
+          t.setDaemon(true);
+          return t;
+        });
     threadPool.setRemoveOnCancelPolicy(true);
     return wrap(container, new VirtualScheduledExectuorService(threadPool));
   }

operator/src/test/java/oracle/kubernetes/operator/work/FiberTestSupport.java

@@ -1,4 +1,4 @@
-// Copyright (c) 2018, 2023, Oracle and/or its affiliates.
+// Copyright (c) 2018, 2024, Oracle and/or its affiliates.
 // Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl.
 
 package oracle.kubernetes.operator.work;
@@ -284,6 +284,11 @@ int getNumItemsRun() {
       return numItemsRun;
     }
 
+    @Override
+    public void shutdown() {
+      // no-op
+    }
+
     @Override
     @Nonnull
     public ScheduledFuture<?> schedule(