UP-3613: Shibboleth and attributes user caching - Workaround

Here a Workaround for the UP-3613
https://issues.jasig.org/browse/UP-3613

I make a PR here even if I know that this commit is useful only for an uPortal with sibboleth authentication and affects performance for others.

So don't hesitate to refuse the PR of course ;) (just a workaround here) 
The issue can be a real problem here for an uportal + shibboleth installation.

Thank you.
Vincent.