libweston: Reset repaint schedule for all repainted outputs when repaint cancel

All outputs is canceled repaint when a output repaint is failed. At that
time, the output whose repaint is success is not scheduled because the
repaint status of that is still REPAINT_AWAITING_COMPLETION. Therefore,
we need to reset repaint schedule for all repainted outputs.

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>