Update SstFileWriter to use bottommost_compression if avaliable

Summary: SstFileWriter ignore Options::bottommost_compression, update it to use bottommost_compression if available

Test Plan:
make check -j64
verified used compression using ./sst_dump

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, yoshinorim

Differential Revision: https://reviews.facebook.net/D59841

table/sst_file_writer.cc

@@ -104,10 +104,14 @@ Status SstFileWriter::Open(const std::string& file_path) {
     return s;
   }
 
-  CompressionType compression_type = r->mutable_cf_options.compression;
-  if (!r->ioptions.compression_per_level.empty()) {
+  CompressionType compression_type;
+  if (r->ioptions.bottommost_compression != kDisableCompressionOption) {
+    compression_type = r->ioptions.bottommost_compression;
+  } else if (!r->ioptions.compression_per_level.empty()) {
     // Use the compression of the last level if we have per level compression
     compression_type = *(r->ioptions.compression_per_level.rbegin());
+  } else {
+    compression_type = r->mutable_cf_options.compression;
   }
 
   std::vector<std::unique_ptr<IntTblPropCollectorFactory>>