spec: fix encrypted_cookie_store resetting for selenium

Change-Id: I116364f2817ffad64ce6e9b6abe00337d32e58ef
Reviewed-on: https://gerrit.instructure.com/30465
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>