stop_xwiki.sh does not wait long enough for clean exit

It always says:

Failed to stop XWiki cleanly, attempting kill...

which works but is worrying.

I tried running:

java -Djetty.home=jetty -Djetty.base=/jetty -jar jetty/start.jar --stop STOP.KEY=xwiki STOP.PORT=8079

and it stopped cleanly after 23 seconds, so possibly the 20 second wait needs to be increased.

The server was idle at the time.