title: How to override luigi complete() method so that the underlying task will come to know the previous ones were completed?
body: <p>I have the following tasks :</p>
  
  <pre><code>class TaskA(ExternalProgramTask):
      def program_args(self):
          return ["/simpleScripts/shell5.bash"]
      def program_environment(self):
          env = os.environ.copy()
          return env
  </code></pre>
  
  <p>The shell script is running properly. After this if I try to run any other task , those task will fail by throwing "unfulfilled dependency error" in TaskA. </p>
  
  <p>The reason I understood is usually Luigi will have output() method where a localTarget is created and thus Luigi will come to know that that Task is completed. </p>
  
  <p>Here while running shell script I don't have any localTarget and thus 
  luigi fails to understand whether it is completed or not. How to make this correct ?</p>