Summary:
block_size_deviation is in percentage while the partition size is in bytes. The current code fails to take that into account resulting into very large target size for filter partitions.
Closes https://github.com/facebook/rocksdb/pull/3187

Differential Revision: D6376069

Pulled By: maysamyabandeh

fbshipit-source-id: 276546fc68f50e0da32c462abb46f6cf676db9b2