title: Can't access Airflow default_args
body: <p>I'm new to airflow, can someone please help me with this as I'm unable to access 'db_conn' inside my custom operator, this argument defined in default_args.</p>
  <pre><code>**Dag details:**
  
  default_args = {
      'owner': 'airflow',
      'email': ['example@hotmail.com'],
      'db_conn': 'database_connection'
  }
  
  dag = DAG(dag_id='my_custom_operator_dag', description='Another tutorial DAG',
            schedule_interval='0 12 * * *',
            start_date=datetime(2020, 8, 6), 
            catchup=False,
            default_args=default_args)
  
  operator_task_start = MyOperator(                                
                                  task_id='my_custom_operator', dag=dag
                                  )
  
  **Operator details:**
  class MyOperator(BaseOperator):
  
      #@apply_defaults
      def __init__(self,
                   *args, 
                   **kwargs):          
          super(MyOperator, self).__init__(*args,**kwargs)
      def execute(self, context):        
          log.info('owner: %s', self.owner)
          log.info('email: %s', self.email)
          log.info('db_conn: %s', self.db_conn) 
          # Error here, AttributeError: 'MyOperator' object has no attribute 'db_conn
  </code></pre>