Validate sudo RunAsUser/RunAsGroup arguments
FreeIPA SUDO rules use --usercat/--groupcat to specify that rule
applies to all users or groups. Thus, sudorule-add-runasuser and
sudorule-add-runasgroup accept specific groups and users and do not
accept ALL reserved word.
The patch validates user and group passed to these commands and
reports appropriate errors when these are ALL.
Ticket #1496
https://fedorahosted.org/freeipa/ticket/1496