In #307, we added the ability to send a stable, static user identifier (i.e. external user ID) to fix failed launches with the QwikLabs tool. This is because the QwikLabs tool did not work with the course-anonymized user IDs we used to send (i.e. anonymous user IDs). Inadvertently, this change broke the LTI 1.1 Basic Outcomes Service and the LTI 2.0 Result Service for courses that use the external user ID (i.e. they have the lti_consumer.enable_external_user_id_1p1_launches CourseWaffleFlag enabled). The Basic Outcomes Service and Result Service handle grade pass backs. Because we now have two ways to identify a user in LTI 1.1/2.0, we must update the Basic Outcomes Service and Result Service to support both. This commit fixes this bug.

This is just to keep it in line with other xblocks that define
an is_past_due attribute. Nicer if they all have the same access
pattern.

Updated to run tests on both python 2 and 3.

PROD-774