fix delayed jobs shard activation for rails 3

Change-Id: Id24b40d05d9917e768923100e197eec31d7804a2
Reviewed-on: https://gerrit.instructure.com/30843
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>