Add a new project property "withDocker" on the Qbs build
Add a new project property "withDocker" on the Qbs build

This allows developers to build Qbs with --all-products on a system that
has Docker installed, but without building the Docker images, since this
can take a very long time.

Change-Id: Idc0514e8d603311559125beba4b14b352613adcd
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs