create summary messages on the user's shard

Change-Id: I35324dac349907031c0737a8eb9f4d2f9444255f
Reviewed-on: https://gerrit.instructure.com/30090
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>