QDateTime - Use the copy constructor in addDays/Months/Years

Currently the QDateTime::addDays/Months/Years methods copy all the
d member variables themselves, but this is bad practice as it means 3
more places where we have to get the copy code correct.  Instead use
the copy constructor to do what it's meant to.  This saves more changes
when we add proper OffsetFromUTC and TimeZone support.

Change-Id: Ie2641d0cb58405335206edcce2e2db30702b78bf
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
QNetworkReply auto test: adapt to new session life time

... supported on the new test server. Once the new server image is in
place, we can only allow for the new life time hint of 300 seconds.

Task-number: QTBUG-33040
Change-Id: Id6ad9983789cc6badf3fc2f6628bf79379988201
Reviewed-by: Richard J. Moore <rich@kde.org>