Adding timer instrumentation for BatchSplitter and RollupTypeCacher

https://jira.rax.io/browse/CMD-355

* Added instrumentation for BatchSplitter and RollupTypeCacher ingestion processors
* Check if any other processors need that instrumentation 
* Check if any tests need to be added
@dlobue 

I modeled this after BatchWriter -
https://github.com/rackerlabs/blueflood/blob/master/blueflood-core/src/main/java/com/rackspacecloud/blueflood/inputs/processors/BatchWriter.java#L69

Is there a reason why we are not starting the timer in the Callable in this case?