ipaserver/install/adtrust.py: Do not use DOMAIN_LEVEL_0 for minimum
As there is the minimal domain level setting MIN_DOMAIN_LEVEL, it should
be used instead of DOMAIN_LEVEL_0.
See: https://pagure.io/freeipa/issue/7669
Signed-off-by: Thomas Woerner <twoerner@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>