it's safe to use OneMerge.getTotalBytesSize (fixed in LUCENE-4775)
Fix for benchmark test

- Fix bug where repeatedly calling computeSummaryStatistics() could
  accumulate some values incorrectly.
- Fix check for number of responsive nodes on list is <= number of
  candidate benchmark nodes.
- Add public getters for summary statistics
- Add javadoc for new getters
- Add javadoc comments about API use