Storage cache seems to be cleaned after coin restart

Before coin restart e.g webengine builds found proper qtbase artifacts, see http://10.212.3.36:8080/coin/integration/qt/qtwebengine/tasks/1550794851

After restart it isn't the case anymore, see http://10.212.3.36:8080/coin/integration/qt/qtwebengine/tasks/1550834465

Similar issues with other submodules, at least with qt3d (http://10.212.3.36:8080/coin/integration/qt/qt3d/tasks/1550837274)