IPA SUDO: support old ipasudocmd rdn
FreeIPA versions older than 3.1 have rdn sudoCmd instead of ipaUniqueID.
Resolves:
https://fedorahosted.org/sssd/ticket/2969
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
(cherry picked from commit 84060f52e782b079337ee7a99bb7ad17e8c84fbb)