Summary:
This branch extends existing property map which keeps values in doubles to keep values in strings so that it can be used to provide wider range of properties. The immediate need for that is to provide IO stall stats in an easy parseable way to MyRocks which is also part of this branch.
Closes https://github.com/facebook/rocksdb/pull/2794
Differential Revision: D5717676
Pulled By: Tema
fbshipit-source-id: e34ba5b79ba774697f7b97ce1138d8fd55471b8a
8a6708f5f2