redis jobs for rails 3

since we're not inheriting from AR::Base, we have to implement some more
stuff ourself. still better than getting all of AR::Base, though.

Change-Id: Ifb21966310b90864394e135d97f1bef1ed6650a4
Reviewed-on: https://gerrit.instructure.com/30254
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>