rails4: gemify delayed_job

closes CNVS-14275

While we're at it, fix all the rspec deprecation warnings.

test plan: delayed jobs should still work as before, including queuing,
viewing in the UI, and running.

Change-Id: I36c6b74aa2b59a99e4f1f36e25e6d0e9e153f92a
Reviewed-on: https://gerrit.instructure.com/41211
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>