public String toString(){
    return String.format("LlapThreadLocalStatistics: %s", schemeToThreadLocalStats.toString());
  }
Merges the list to a map.
Input list:
1. FileSystem.Statistics (scheme: file)
2. FileSystem.Statistics (scheme: hdfs)
3. FileSystem.Statistics (scheme: hdfs)
Output map:
file : LlapThreadLocalStatistics.StatisticsData (1)
hdfs : LlapThreadLocalStatistics.StatisticsData (2 + 3)
llap-common/src/java/org/apache/hadoop/hive/llap/LlapThreadLocalStatistics.java