If a size is defined in the VSM for a container with VStack or HStack as children presentation type, this can lead to a useless scroll bar.
Steps to reproduce:
* Imports the project from compartments.zip (https://bugs.eclipse.org/bugs/attachment.cgi?id=262135 from bug 495046)
* Open the diagram VStackDiag
* Use the tool EPackage to create a package container on the diagram with default size (only one click on the diagram)
* Use the tool EClassList to create a class in the package
* KO: A scroll bar appears in the container.
Another steps to reproduce:
* Use same diagram
* Use the tool EPackageWithOneClass to create a package container with a class inside it with default size (only one click on the diagram)
* KO: A scroll bar appears in the container.
This scroll bar does not disappear even if the container is resized.
The problem does not exist if the size of the VStack container mapping defined of the VSM is {-1, -1} instead of {5, 5}.
If the size is set to {10, 10}, we have a problem similar to bug 495046:
* The height of the container is not of 100 pixels.
* The width of the class is not fit to the width of the container.
