Move the wl_output global management into weston_compositor_add_output()
and weston_compositor_remove_output().
If weston_output_enable() fails, there is no need to clean up the global
and the clients will not see a wl_output come and go.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Armin Krezović <krezovic.armin@gmail.com>