This diff modifies webconnectivity@v0.5 to take decisions regarding
TLS blocking by using the response from the TH rather than using
questionable heuristics based on inspecting the TLSHandshake list
alone. This change should improve correctness _when_ we're using
the improved TH, which is currently used for 50% of the probes.
See https://github.com/ooni/probe/issues/2257
While there, modify `control.go` to specify which control is being used.
