IPA: do not try to save override data for the default view
    
    For the default view all override data is available in the cached user
    or group object. Even if separate override data is available it should
    not be written into the cache.
    
    Resolves https://fedorahosted.org/sssd/ticket/2630
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>