fix role overrides fetching for site admin on a separate shard

test plan:
* have site admin on one shard
* make a custom account role
* give it all the permissions
* login as a user with that custom role
* visit an account on another shard
* should have all the permissions

Change-Id: I2a128a672b7b6973e1d25c58d635f0147a486240
Reviewed-on: https://gerrit.instructure.com/44353
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>