test: fix thread leak in StreamingSubscriberConnectionTest and make threadB daemon in ClientConfigurationManagerTest

Author: jinseopkim0

java-bigtable/google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/internal/util/ClientConfigurationManagerTest.java

@@ -359,6 +359,7 @@ public void onChange(SessionClientConfiguration newValue) {
                 }
               }
             });
+    threadB.setDaemon(true);
     threadB.start();
 
     // Wait for Thread B to acquire the alien lock

java-pubsub/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/StreamingSubscriberConnectionTest.java

@@ -101,13 +101,15 @@ public class StreamingSubscriberConnectionTest {
   @Before
   public void setUp() {
     systemExecutor = new FakeScheduledExecutorService();
+    executor = new FakeScheduledExecutorService();
     clock = systemExecutor.getClock();
     mockSubscriberStub = mock(SubscriberStub.class, RETURNS_DEEP_STUBS);
   }
 
   @After
   public void tearDown() {
     systemExecutor.shutdown();
+    executor.shutdown();
   }
 
   @Test