Quiz index: auto-grade all outstanding course subs

Closes CNVS-15402

TEST PLAN
---- ----

  - create 2+ quizzes in a course
  - make some submissions, don't turn them in
  - go to quizzes index
  - verify your submissions are now graded (you may have to wait a bit
    since it's done in a background job)

Change-Id: I80af5523f7549120ca81a5029d9681ddd511bb2b
Reviewed-on: https://gerrit.instructure.com/40862
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ryan Taylor <rtaylor@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>