title: Airflow error during celery execution
body: <p>We have an airflow setup with rabbitmq, mysql db and celery executor setup in a docker instance.
  Trigerring the first individual step/opertator via a run command as below works.</p>
  
  <pre><code>airflow run wfm_model_training_client_1_queue_11 fetch_top_funnel_data  2016-03-03
  </code></pre>
  
  <p>However when we trigger the entire dag via a backfill command as below, we encounter the following error during celery execution. Clearly this is an error with celery, however how do i extract more logs to debug the same.</p>
  
  <p>backfill command</p>
  
  <pre><code>airflow backfill wfm_model_training_client_1_queue_11 -s 2016-03-03 -e 2016-03-03
  </code></pre>
  
  <p>Celery error in celery_taskmeta table in traceback column</p>
  
  <pre><code>Traceback (most recent call last):
    File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 367, in trace_task
      R = retval = fun(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/celery/app/trace.py", line 622, in __protected_call__
      return self.run(*args, **kwargs)
    File "/usr/lib/python2.7/site-packages/airflow/executors/celery_executor.py", line 59, in execute_command
      except subprocess.CalledProcessError as e:
  AirflowException: Celery command failed
  </code></pre>