Testconfig: Forcing macx-clang_developer-build_OSX_10.8 to succeed

This property was missing from Qt5_release_Integration while deployed
the stage to all projects.

Change-Id: I9dc094f2924b4cd68ce00f3a9b938c82ae339b49
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>