Add missing #setBreaker setter to NodesStatsRequestBuilder
Encapsulate Operations on SegmentReader in a utils class

This commit adds support to extract SegmentReader instances from
FilteredAtomicReader instances to support reader wrapping in
caches as well.
Fix RandomExceptionCircuitBreakerTests

RandomExceptionCircuitBreakerTests never actually installed
the FilteredAtomicReader that should throw random exceptions
when field data is loaded.
Add better error reporting if a json spec can not be parsed
Add missing closing '}' to indices.stats.json