fix coll scan in aggregation query
fix coll scan in aggregation query

because of a mongodb bug that prevents using available index
in $expr $in in aggregation pipeline

https://jira.mongodb.org/browse/SERVER-32549
https://jira.mongodb.org/browse/SERVER-37470

Revert this when the mongodb bug is fixed, for additional perf

luanlv/lila,arex1337/lila,arex1337/lila,luanlv/lila,arex1337/lila,luanlv/lila,luanlv/lila,arex1337/lila,luanlv/lila,arex1337/lila,luanlv/lila,arex1337/lila,arex1337/lila,luanlv/lila