Code review comment for lp:~widelands-dev/widelands/ai_productionsites_statistics

AI need % of building utilization. And I think showed % (in UI) is not reliable enough...
By old approach it just presumed that successful program took 5x more than unsuccessful program - this is example. With exact timing the number would be more exact.
Also we have 'skipped' and 'failed' programs that takes various time I think.
This change guarantee that whatever changes to productions programs this code will not need an update...