refactor(webconnectivity@v0.5): improve logging clarity (#964)

We're bumping the experiment's version number because we changed the name of the field used to contain late/duplicate DNS responses. We have also changed the algorithm to determine `#dnsDiff`. However, the change should only impact how we log this information. Overall, here the idea is to provide users with a reasonably clear explanation of how the probe maps observations to blocking and accessible using expected/unexpected as the conceptual framework.

Part of https://github.com/ooni/probe/issues/2237

internal/experiment/webconnectivity/analysishttpcore.go

@@ -53,10 +53,10 @@ func (tk *TestKeys) analysisHTTPToplevel(logger model.Logger) {
 			netxlite.FailureEOFError:
 			tk.BlockingFlags |= analysisFlagHTTPBlocking
 			logger.Warnf(
-				"HTTP: endpoint %s is blocked (see #%d): %s",
+				"HTTP: unexpected failure %s for %s (see #%d)",
+				*failure,
 				finalRequest.Address,
 				finalRequest.TransactionID,
-				*failure,
 			)
 		default:
 			// leave this case for ooni/pipeline