Unit testcase demonstrating extruding from internal faces
(using a faceZone instead of a faceSet)

- pass 1 :  extrude on bottom left cell both internal faces and a boundary face.
            These faces will all be extruded away from cell 0 (i.e. no flip in
            the faceZone)

- pass 2 :  extrude on top right cell both internal and boundary faces.
            The internal faces will all have flip in the faceZone)