tst_http2::connectToHost - fix flakiness

some assumptions were incorrect: our test server immediately sends
its SETTINGS frame, as a result we have to reply with client preface +
SETTINGS(ACK). So QVERIFY(!prefaceOK) was wrong from the beginning and
was only passing by pure luck.

Change-Id: Ie43f0d4ac41deb0e5339badaae6149a9b2f9d9b3
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

tests/auto/network/access/http2/BLACKLIST

@@ -1,3 +0,0 @@
- See qtbase/src/testlib/qtestblacklist.cpp for format
-[connectToHost]
-*

tests/auto/network/access/http2/tst_http2.cpp

@@ -648,9 +648,6 @@ void tst_Http2::connectToHost()
         eventLoop.exitLoop();
         QCOMPARE(reply->error(), QNetworkReply::NoError);
         QVERIFY(reply->isFinished());
-        // Nothing must be sent yet:
-        QVERIFY(!prefaceOK);
-        QVERIFY(!serverGotSettingsACK);
         // Nothing received back:
         QVERIFY(reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).isNull());
         QCOMPARE(reply->readAll().size(), 0);