@Override
  public List<Task<?>> getDependentTasks() {
    return listTasks;
  }
Add a dependent task on the current conditional task. The task will not be a direct child of
conditional task. Actually it will be added as child task of associated tasks.

@return true if the task got added false if it already existed
ql/src/java/org/apache/hadoop/hive/ql/exec/ConditionalTask.java