TODO The only problem with these counters would be on restart.
The jobtracker updates the counter only when the task that is scheduled
if from a non-running tip and is local (data, rack ...). But upon restart
as the reports come from the task tracker, there is no good way to infer
when exactly to increment the locality counters. The only solution is to
increment the counters for all the tasks irrespective of
- whether the tip is running or not
- whether its a speculative task or not

So to simplify, increment the data locality counter whenever there is
data locality.