Change the default renderTarget and renderStrategy

Change the default renderTarget and renderStrategy

As we always use OpenGL and scenegraph render thread now, the best default
render target should be FBO and the best render strategy should be
cooperative mode (use the render thread).

Task-number:QTBUG-23956
Change-Id: I64b070dec566e359d27c84680fef1c691d6ce411
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>