adtrust-install: Correctly determine 4.2 FreeIPA servers
We need to detect a list of FreeIPA 4.2 (and above) servers, since
only there is the required version of SSSD present.
Since the maximum domain level for 4.2 is 0 (and not 1), we can filter
for any value of ipaMaxDomainLevel / ipaMinDomainLevel attributes
to generate the list.
https://fedorahosted.org/freeipa/ticket/5199
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>