explicitly include the app center access token in the cache key

Test Plan:
 - Set up an organization on eduappcenter with a whitelist
 - Generate two tokens for the organization
 - Launch app center in canvas with the first access token
 - Quickly change the whitelist
   * The apps should match the original whitelist (no change)
 - Quickly update the access token in canvas plugin settings
    * The apps should match the updated whitelist

fixes PLAT-362

Change-Id: I652add4a993a0c6afdc4ff6b9a138efeb933c32a
Reviewed-on: https://gerrit.instructure.com/30611
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>