DisMaxQueryBuilder的定义：
A query that generates the union of documents produced by its sub-queries, and that scores each document with the maximum score for that document as produced by any sub-query, plus a tie breaking increment for any additional matching sub-queries.
就是DisMaxQueryBuilder可以用来查找出 最高的几个 分数的doc，
注意是，这几个 最高分的分值是相同的，
如果只有一个 最高分的doc就只返回一个doc