DS Quiz Moderate - Show proper extra allotted time

Closes CNVS-2143

TEST PLAN
---- ----

  - create a quiz with no questions, set a time limit
  - visit the moderate page (DS, not ember)
    + click the little pencil/edit icon next to a student row of your
      choice
      - give them like 3 extra minutes for each attempt
        + verify you see "gets 3 extra minutes on each attempt" in the
          block
    + do it again, give them 0 minutes
      - verify the message disappears
    + rinse and repeat with different inputs for different students,
      it should always update properly

Change-Id: I0f8724b95221f52d6eba94577fcbae1bfd47d1b8
Reviewed-on: https://gerrit.instructure.com/38418
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>