more optimization for scheduler

closes CNVS-12936

test plan:
 * basic regression test of scheduler functionality

Change-Id: I7cd7de55e36a66e18fdf01de85d0240bee69c437
Reviewed-on: https://gerrit.instructure.com/34555
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>