QNAM - fix poor performance of HEAD request with authentication

QHttpNetworkReply was waiting for a body to be sent for 401 and 407
responses, whereas with a HTTP HEAD request, there will be no body.

This delayed the authentication signal until after the http channel
is closed by the server after a timeout. For example with the server
used for autotesting, the authentication signal is delayed 15 seconds.

When the server has a very long timeout, the authentication signal may
not be emitted at all.

Task-Number: QT-5304
Reviewed-By: Martin Petersson
(cherry picked from commit 8610ee14b8636641651a8ba6040cca16c4141ed6)

Change-Id: Ie4ce6c598df86ce59910f793fd5ae7c1ccf39f9d
Reviewed-on: http://codereview.qt-project.org/6032
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Petersson <Martin.Petersson@nokia.com>

src/network/access/qhttpnetworkreply.cpp

@@ -814,7 +814,7 @@ bool QHttpNetworkReplyPrivate::expectContent()
         || statusCode == 204 || statusCode == 304)
         return false;
     if (request.operation() == QHttpNetworkRequest::Head)
-        return !shouldEmitSignals();
+        return false; // no body expected for HEAD request
     qint64 expectedContentLength = contentLength();
     if (expectedContentLength == 0)
         return false;