title: Airflow throw an error on filling up the DagBag while "airflow resetdb", before tables created
body: <p>I am using Airflow to build dags dynamically.
  The dag builder uses "variable" to get and set values.</p>
  
  <p>When I am running "airflow resetdb", Airflow throw an error: "(psycopg2.ProgrammingError) relation "variable" does not exist".</p>
  
  <p>I see that Airflow Filling up the DagBag while "airflow resetdb" and before the tables created.</p>
  
  <p>Why airflow running "Filling up the DagBag", while "airflow resetdb"?</p>
  
  <p>Is there any way to solve it?</p>