don't unnecesarily dirty rows

this data actually changes rarely, so don't force the row to be written
if it didn't change

Change-Id: I7876ab5488f8b0d810f032f20bc5a60c06447efd
Reviewed-on: https://gerrit.instructure.com/28995
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>