point-to-point-layout: Respect absolute values of specified boundaries

Before the change, the values specified in SetBoundaryBox were used only
to calculate relative positions of grid nodes.

src/point-to-point-layout/model/point-to-point-grid.cc

@@ -217,7 +217,7 @@ PointToPointGridHelper::BoundingBox (double ulx, double uly,
               loc = CreateObject<ConstantPositionMobilityModel> ();
               node->AggregateObject (loc);
             }
-          Vector locVec (xLoc, yLoc, 0);
+          Vector locVec (ulx + xLoc, uly + yLoc, 0);
           loc->SetPosition (locVec);
 
           xLoc += xAdder;