fix switchman shard migration for rails 2

Change-Id: If185cfa0cefe901deb3372bb50496e0dbf02bab4
Reviewed-on: https://gerrit.instructure.com/29645
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>