Added task reconciliation.

@airbnb/di 
There are actually already some metrics, but not pertaining to this particular feature.

See:

https://github.com/airbnb/chronos/blob/master/src/main/scala/com/airbnb/scheduler/jobs/JobStats.scala
https://github.com/airbnb/chronos/blob/master/src/main/scala/com/airbnb/scheduler/jobs/JobMetrics.scala