Implement HTTP Host
This involves changing the Host header field of an HTTP request to that of the site one wishes to check for censorship.
This test is already properly specified here: https://trac.torproject.org/projects/tor/wiki/doc/OONI/Tests/HTTPHost.
There is a previous implementation of it inside of the old-to-be-converted directory of OONI probe. We need to expand that to include everything inside of the specification and port it to the new twisted friendly model.
We also have the unanswered question of how do we detect that a page is a blockage page?.