1973 - Disable BROKER_USE_SSL for MongoDB Result Backend

This should fix celery/celery#1973.

This change effectively disables SSL as set using BROKER_USE_SSL.  SSL support should be functional through existing mechanisms, but requires doc changes and testing.  I've documented this potential feature and the necessary work with celery/celery#1974

This is a very small change to get into the authors file, but I plan to make more in the future.