"staticstub" system test: make root hints consistent with authoritative data

The ns2 named instance in the "staticstub" system test is configured with a single root hint commonly used in BIND system tests (a.root-servers.nil with an address of 10.53.0.1), which is inconsistent with authoritative data served by ns1. This may cause intermittent resolution failures, triggering false positives for the "staticstub" system test. Prevent this from happening by making ns1 serve data corresponding to the contents of bin/tests/system/common/root.hint.