@Override
  public boolean closeConnection(StatsCollectionContext scc) {
    return true;
  }
An test implementation for StatsAggregator.
aggregateStats prints the length of the keyPrefix to SessionState's out stream
All other methods are no-ops.
itests/util/src/main/java/org/apache/hadoop/hive/ql/stats/KeyVerifyingStatsAggregator.java