Fix tst_QNetworkReply::httpWithNoCredentialUsage autotest

Fix tst_QNetworkReply::httpWithNoCredentialUsage autotest

The test was testing the wrong thing, and passing even though
QNetworkRequest::AuthenticationReuseAttribute was not being
respected, until recently when I fixed username/password in URLs

Now the cache is properly bypassed when this attribute is set to
manual, and the autotest is updated to check this.

Change-Id: I87943515562d0b16b03504f0758ba265758d1c22
Reviewed-by: Martin Petersson <Martin.Petersson@nokia.com>