Stabilize CustomNotificationListenerTest

org.jbpm.springboot.samples.CustomNotificationListenerTest.testProcessEventListenerRegistration is failing sometimes because CountDownLatchNotificationListener uses a saveContent attribute that has been set to true previously in other test.

java.lang.IllegalStateException: EntityManagerFactory is closed at org.hibernate.internal.SessionFactoryImpl.validateNotClosed(SessionFactoryImpl.java:531) at org.hibernate.internal.SessionFactoryImpl.createEntityManager(SessionFactoryImpl.java:613) at org.hibernate.internal.SessionFactoryImpl.createEntityManager(SessionFactoryImpl.java:154) at sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.invokeProxyMethod(AbstractEntityManagerFactoryBean.java:497) at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean$ManagedEntityManagerFactoryInvocationHandler.invoke(AbstractEntityManagerFactoryBean.java:680) at com.sun.proxy.$Proxy146.createEntityManager(Unknown Source) at org.jbpm.shared.services.impl.TransactionalCommandService.execute(TransactionalCommandService.java:71) at org.kie.spring.jbpm.services.SpringTransactionalCommandService.execute(SpringTransactionalCommandService.java:74) at org.jbpm.kie.services.impl.RuntimeDataServiceImpl.getTaskById(RuntimeDataServiceImpl.java:806) at org.jbpm.kie.services.impl.UserTaskServiceImpl.saveContent(UserTaskServiceImpl.java:707) at org.jbpm.kie.services.impl.UserTaskServiceImpl.saveContent(UserTaskServiceImpl.java:703) at org.jbpm.kie.services.impl.UserTaskServiceImpl.saveContent(UserTaskServiceImpl.java:693) at org.jbpm.springboot.samples.events.listeners.CountDownLatchNotificationListener.onNotification(CountDownLatchNotificationListener.java:60) at org.jbpm.services.task.deadlines.notifications.impl.NotificationListenerManager.broadcast(NotificationListenerManager.java:132)