Our authentication code is race-y by design:
1. When two requests are fired off and queued at the same time in the
same QHttpNetworkConnection then if one of them encounters
"authentication required" then it will copy whatever credentials it got
to all the other channels in the connection. This is likely what the
first part of the test is testing.
2. If a later request is fired off and it includes credentials in the
url then the newly included credentials should be used instead of the
cached ones.

The race here can occurr when one socket either takes too long to
connect or the connected signal is not received early enough. Then the
first socket is used for both requests and then we can hit case #2 when
the url contains credentials.

Change-Id: I646a5378d8c1256b2de98b51912953df29f68cb2
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit 5a47939)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>