Loader: don't create a configuration for every group
Loader: don't create a configuration for every group

Groups that do not set any module / product properties can reuse the
product's configuration.

Change-Id: I38bc11ad3ebd42d8ae4a476ea89523b69ef8e006
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@nokia.com>

qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,villytiger/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,villytiger/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,Distrotech/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,qt-labs/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,villytiger/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs