make product.buildDirectory available in Probe item

As a consequence product.name is evaluated very early and cannot depend
on module properties and such. Autotests that used product.name as
verification script had to be adjusted accordingly.

Task-number: QBS-393
Change-Id: I62ae1a92313af54d9eb15e88b7457388584f7556
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>