Fix rare "allow-query" system test failures

In the "allow-query" system test, ns3 uses a root hints file which contains a single entry for a.root-servers.nil (10.53.0.1). This name is not present in the root zone served by ns1, which means querying it for that name and any type will yield an NXDOMAIN response. When combined with unfavorable thread scheduling, this can lead to ns3 caching an NXDOMAIN response for the only root server it is aware of and thus to false positives for the "allow-query" system test caused by ns3 returning unexpected SERVFAIL responses. Fix by modifying the root zone served by ns1 so that authoritative responses to a.root-servers.nil queries match the root hints file used by ns3.