spec: make accounts controller spec less fragile

Change-Id: I75472193dda09bb1881ebaf099c382622aaf3ddc
Reviewed-on: https://gerrit.instructure.com/29183
Reviewed-by: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>