Testconfig: Disable build publishing to builds.qt-project.org

We are running out of diskspace in builds.qt-project.org. Disabling
build publishing until we have more space.

Change-Id: I91b2a900da668c3b6053e47d4e98b4549051e8ab
Reviewed-by: Simo Fält <simo.falt@digia.com>