clear shard and special account caches based on age

test plan:

- regression test to make sure that you can navigate to different
  domains and shards, create + process delayed jobs, and navigate to the
  default and site admin accounts

Change-Id: I0ed4bf3309e3950a046ed1cd7bc7b1fe0a806a7a
Reviewed-on: https://gerrit.instructure.com/39972
Tested-by: Brian Palmer <brianp@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>