delayed_jobs extensions for sharding in rails 3

Change-Id: Ic533c19fb4c54ca3de2acb4265b2d884036e28f6
Reviewed-on: https://gerrit.instructure.com/29442
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>