"filter-aaaa" system test: make root hints consistent with authoritative data

Resolvers in the "filter-aaaa" system test are configured with a single root hint: "ns.rootservers.net", pointing to 10.53.0.1. However, querying ns1 for "ns.rootservers.net" results in NXDOMAIN answers. Since the TTL for the root hint is set to 0, it may happen that a resolver's ADB will be asked to return any known addresses for "ns.rootservers.net", but it will only have access to a cached NXDOMAIN answer for that name and an expired root hint, which will result in a resolution failure, triggering a false positive for the "filter-aaaa" system test. Prevent this from happening by making all the root hints consistent with authoritative data served by ns1.