Use mapped attributes for nameid detection
    
    This moves up the attribute mapping to before finding the NameID,
    which allows remapping of username or email fields used for NameID
    with the default attribute mapping schemes.
    
    Ticket: #208
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Rob Crittenden <rcritten@redhat.com>