test-k8s: move start_date and catchup kwargs to the DAG init arguments

According to https://airflow.apache.org/docs/apache-airflow/stable/_api/airflow/models/dag/index.html#airflow.models.dag.DAG these arguments should be passed to the DAG class constructor.

That explains why the s3 connection test DAG ran 60 times when I deployed it, even though I had catchup: False in the default args.

Signed-off-by: Balthazar Rouberol brouberol@wikimedia.org