Exclude mirrors returning cloudflare pages from latency tests

[nroi]

Some mirrors put cloudfront in front of the actual server, so the response we obtain in our latency test is not necessarily a response from the actual server, but from cloudflare. This is a problem if cloudware does not return the actual content, but instead asks the user to enter a captcha. This means that:

1. This mirror is completely unsuited as a mirror because it requires the user to enter a captcha before starting the download, and
2. The latency result is completely useless, because we intend to measure the latency to the actual server, not to cloudflare.