Fix cache problem when non admin users access the site.

There is a bug in the cern_toolbar that caches the username and users
visiting see other people's usernames. This causes major confusion. To
reproduce it I needed to create two service accounts that do not have
administrator access.
Steps to reproduce:
 - in a private window login with srvaccount1
 - observe srvaccount1 in the toolbar and close the private window
 - in a new private window login with srvaccount2
 - observe srvaccount1 in the toolbar again