QNX: Fix QMdiWindow autotests

In "setOpaqueResizeAndMove" this patch makes sure that the content of a subwindow
actually fits into the window, otherwise the resize does not work properly.
The content is dpi dependent and thus the pixel size of it increases with the display
dpi value.
Furthermore when moving the QMdiSubwindow this patch makes sure that we actually grab
the window's header and not one of it's tool buttons (minimize, maximize, close).

Change-Id: I88314994957c5883f57c09c9240a3b83f1ee42ed
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>
Reviewed-by: Bernd Weimer <bweimer@blackberry.com>