cache_req: do not lookup views if possible
    
    This is needed for LOCAL view but also creates a shortcut for
    server side overrides.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2849
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 5f2b1986a16a394ecbecd16f82c7265b5b47b546)