change strategy for ensuring correct shard from relation

just putting it in the scope meant foreign keys got messed up

Change-Id: Ib268df60b4b13dad1f3646e8572c25443b4f1847
Reviewed-on: https://gerrit.instructure.com/30820
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>