add region to cache keys that depend on region

it shouldn't matter, but protects against server misconfiguration

Change-Id: Ic8da4caa9b99e82fa73c4a6e18b1599998da29cd
Reviewed-on: https://gerrit.instructure.com/43224
Reviewed-by: James Williams  <jamesw@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>