Summary:
While writing tests for dynamic Universal Compaction options, I found that the compaction reasons we set for size-ratio based and sorted-run based universal compactions are swapped with each other. Fixed it.
Closes https://github.com/facebook/rocksdb/pull/3412

Differential Revision: D6820540

Pulled By: sagar0

fbshipit-source-id: 270a188968ba25b2c96a8339904416c4c87ff5b3