re-set canonical principal name on migrated users
    
    The migration procedure has been updated to re-set `krbcanonicalname`
    attribute on migrated users as well as `krbprincipalname` so that migration
    from FreeIPA versions supporting principal aliases does not break subsequent
    authentication of migrated users.
    
    https://fedorahosted.org/freeipa/ticket/6101
    
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>