Follow-up v9 experiment

[k88hudson]

In our last experiment, we saw that although the order of queries didn't seem to impact the NEW* failure rate, there was a noticeable difference between queries to dnssec-experiment-moz.net and any subdomain (either the per-client ones or the shared ones).

I think we could run one more experiment to test a few possible theories:

1. There is some kind of behavior that differs for subdomains vs the apex domain
2. There is something about the DNS requests from the fetch request and/or the webext requests that result in cache contamination that our custom A queries do not cause
3. There is something specific to dnssec-experiment-moz.net