LP1972928: Show course user role dropdown choices without typing

LP1972928: Show course user role dropdown choices without typing

To test:
1. Go to Admin > Local Admin > Course List
2. Choose a course
3. Go to the Course users tab
4. Activate the Role dropdown.
5. Note that no options appear.
6. Apply the patch
7. Repeat steps 1-5
8. Note that the role options appear when you activate the dropdown now

Signed-off-by: Jane Sandberg <js7389@princeton.edu>
Signed-off-by: Jennifer Pringle <jennifer.pringle@bc.libraries.coop>
Signed-off-by: Stephanie Leary <stephanie.leary@equinoxOLI.org>