title: Celery periodic tasks does not execute
body: <p>I am using cloud 9 online IDE for python dev.
  Here's my code:</p>
  
  <pre><code>from celery import Celery
  from celery.schedules import crontab 
  from datetime import timedelta
  
  RESULT_URL = 'mongodb://********' 
  BROKER_URL = 'redis://*********'
  
  app = Celery('tasks', backend=RESULT_URL,broker=BROKER_URL)
  CELERY_TIMEZONE = 'UTC'
  
   CELERYBEAT_SCHEDULE = {
  'add-every-30-seconds': {
      'task': 'tasks.add',
      'schedule': timedelta(seconds=30),
      'args': (16, 16)
  },
  }
  
  @app.task
  def add(x, y):
      print x+y
      return x + y
  </code></pre>
  
  <p>And I am starting it out with the command:</p>
  
  <pre><code>celery -A tasks worker --loglevel=info --beat
  </code></pre>
  
  <p>Celery starts OK,but stops all activity there.Manually invoked tasks work fine.
  Here's the console log:</p>
  
  <pre><code>[2015-04-16 07:53:30,954: INFO/Beat] beat: Starting...
  [2015-04-16 07:53:32,696: INFO/MainProcess] Connected to redis://*******
  [2015-04-16 07:53:34,722: INFO/MainProcess] mingle: searching for neighbors
  [2015-04-16 07:53:37,685: INFO/MainProcess] mingle: all alone
  [2015-04-16 07:53:40,343: WARNING/MainProcess] celery@*****-demo-project-563148 ready.
  </code></pre>
  
  <p>I am using RedisLabs free-version as  the Broker and a self hosted mongo as the backend storage. Where am I going wrong?</p>