use a single query instead of n queries to fetch latest account reports

refs CNVS-11420

test plan:
 * run an account report
 * refresh the settings page
 * it should show that it ran

Change-Id: Ie60570db1ceaff51a4dadd0c30357c333dcabf1c
Reviewed-on: https://gerrit.instructure.com/30995
Reviewed-by: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>