Do not try to evaluate examples or demos for Qt 5.

There is no good plan on how to expose examples and demos
of Qt 5 other than using XML manifests. Thus, it's best
to disable the fallback mechanism, as it can only break
(see e.g. QTCREATORBUG-5472).

Change-Id: I4cc1fa875297c3d368ae261f5404fa61301f172f
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>