Export CONFIG and QT_CONFIG from qconfig.pri to QBS.

Task-number: QBS-397
Change-Id: I9b29781e752176d0cf71221b896a6ac017538c7b
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>