Mark xfail for test_is_user_filtered
As fix is not available in f27 marking test as xfail.
reason: https://pagure.io/SSSD/sssd/issue/3978
Signed-off-by: Anuja More <amore@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>
Reviewed-By: Sergey Orlov <sorlov@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>