[FIX] point_of_sale: don't launch Firefox before Odoo has started

When using Wi-Fi the Odoo instance on the POSBox will start after a
Wi-Fi connection is established. This takes a bit longer than when
you're using a wired connection. If Firefox gets started before you
end up with a 'Could not connect to localhost:8069' error.

addons/point_of_sale/tools/posbox/overwrite_after_init/etc/xdg/openbox/autostart

@@ -3,4 +3,11 @@ xset s off
 xset -dpms
 
 export HOME=/tmp
-/usr/bin/firefox http://localhost:8069/point_of_sale/display &
+
+DISPLAY_URL='http://localhost:8069/point_of_sale/display'
+
+# wait until odoo is ready, otherwise you will have to plug a
+# keyboard into the posbox just to refresh firefox
+until wget -q "${DISPLAY_URL}" -O /dev/null ; do sleep 1 ; done
+
+/usr/bin/firefox "${DISPLAY_URL}" &