[Groups] Add Test Student

[vlgutier4]

Problem statement:

Problem: The Test Student cannot be enrolled in Groups. Use Case: Instructors are asking how they can "see what someone in a particular group can see in the course". In a cross-listed course that contains both lower- and upper-division sections, an assignment may be assigned to a particular section only. Instructors would like the ability to enroll the Test Student to verify using Student View.

Proposed solution:

Solution: Allow the Test Student to be enrolled in Groups.

User role(s):

instructor,ta,designer