fixes for conversations and sharding for rails 3

Change-Id: I86bde6da2cc006e92c00113dccb95f100c2dadee
Reviewed-on: https://gerrit.instructure.com/29393
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>