Added 'master_name' to 'BROKER_TRANSPORT_OPTIONS_MAP'

[System25]

This option is necessary to use REDIS replication based on sentinels:

[celery]
BROKER_URL = sentinel://:mypassword@sentinel1:26379/1;sentinel://:mypassword@sentinel2:26379/1

[celery:broker_transport_options]
master_name = mymaster

More info in https://github.com/celery/kombu/blob/master/kombu/transport/redis.py (see SentinelChannel).

Thanks