Summary:
Added a test for three dynamic universal compaction options, in the realm of read amplification:
- size_ratio
- min_merge_width
- max_merge_width

Also updated DynamicUniversalCompactionSizeAmplification by adding a check on compaction reason.
Found a bug in compaction reason setting while working on this PR, and fixed in #3412 .

TODO for later: Still to add tests for these options: compression_size_percent, stop_style and trivial_move.
Closes https://github.com/facebook/rocksdb/pull/3419

Differential Revision: D6822217

Pulled By: sagar0

fbshipit-source-id: 074573fca6389053cbac229891a0163f38bb56c4