Map<String, Map<Short, Map<Short, ContainerStorageStats>>> aggregateHostPartitionClassStorageStats(
      Map<String, Map<Long, Map<Short, Map<Short, ContainerStorageStats>>>> storageStatsMap) {
    Map<String, Map<Short, Map<Short, ContainerStorageStats>>> result = new HashMap<>();
    storageStatsMap.forEach((k, v) -> result.put(k, aggregateHostAccountStorageStats(v)));
    return result;
  }
Merge the given map from partition class name to partition id to account id to container id to storage stats, to a
map from partition class name to account id to container id to storage stats. If same account and container exists
in different partitions, then just add storage stats up.
@param storageStatsMap The map of storage stats from partition class name to partition id to account id to container
                       id to storage stats.
@return The map from partition class name to account id to container id to storage stats.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/MySqlClusterAggregator.java