This patch modifies API behavior for
GET /v1.0/actions/{action_id}/steps/{step_id}/logs
such way:
- it returns the same status code as Airflow HTTP request returned
if Airflow responds with a status code of 400 or greater,
- it returns 500 error status code if an exception happens during
Airflow HTTP request (200 was before).
Warning: this change breaks API backward compatibility, now a client
could get 4xx or 5xx codes proxied from Airflow.
Change-Id: Ic5dceb3abc34415d21b4d8d4e71b4e5661a7363d