[AIRFLOW-3704] Support SSL Protection When Redis is Used as Broker for CeleryExecutor (#4521)
[AIRFLOW-3704] Support SSL Protection When Redis is Used as Broker for CeleryExecutor (#4521)

From Celery 4.1 (current Airflow is using 4.1.1),
"broker_use_ssl" argument starts to support Redis
(earlier this argument is only supported when amqp is used for broker)
(REF: https://github.com/celery/celery/blob/4.1/docs/userguide/configuration.rst).
owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow