VID-1120 Reduce the sampling percentage

@Wikia/platform-team @wladekb Here's the change I was proposing in December to limit the profiler samples we take.  I'd like to push this out and monitor New Relic to see if it makes any difference.  Wladek, can you be responsible for checking the mediawiki_profiler DB data to make sure its still enough for our reporting/debugging/etc?