CBQE-1053: changes in bidirectional.load_with_async_ops_and_joint_sets

Change-Id: Ief940ad7f255f3b7ebb38751c463baaa8a933bce
Reviewed-on: http://review.couchbase.org/24701
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>