Testcase test_server_option_with_unreachable_ad creates a zone file
for AD domain. This file had a hard-coded A record for host specified in
NS record. Some versions of BIND consider this zone invalid and refuse
to start with message:
```
zone ad.test/IN: NS 'root-dc.ad.test' has no address records (A or AAAA)
```
Fixed by replacing hard-coded value with short name of the AD instance.
Reviewed-By: Michal Polovka <mpolovka@redhat.com>
f16c08b7d6