After SERVER-37364, the decision is returned once it's majority-committed: the decision promise is emplaced after the TransactionCoordinator waits for the decision to be durable.

This ticket is to emplace the decision promise as soon as the decision is made. Since coordinateCommitTransaction always sets the Client's last OpTime to the system last OpTime before returning the decision, the Client will automatically wait for the user's writeConcern of an OpTime at or later than the decision's OpTime.