Implement DNS lookup Test
This involves doing a DNS lookup for the hostname in question. If the lookup result does not match the expected result the site is marked as being censored.
This test is somewhat already specified here: https://trac.torproject.org/projects/tor/wiki/doc/OONI/Tests/DNSLookup. We need to spec it better using the test template and then port the old version of the test to the new twisted friendly model.