The Gstreamer gstlibcamerasrc element operates better with the
glimagesink, as it can perform direct renders or hardware accellerated
image format conversion.

Further extend the sample commands to demonstrate how to specify a fixed
width and height parameter to the pipeline.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>