fix db_bench argument type

Summary:
it should be a bool
Closes https://github.com/facebook/rocksdb/pull/2653

Differential Revision: D5506148

Pulled By: ajkr

fbshipit-source-id: f142f0f3aa8b678c68adef12e5ac6e1e163306f3

tools/db_bench_tool.cc

@@ -434,7 +434,7 @@ DEFINE_int32(file_opening_threads, rocksdb::Options().max_file_opening_threads,
              "If open_files is set to -1, this option set the number of "
              "threads that will be used to open files during DB::Open()");
 
-DEFINE_int32(new_table_reader_for_compaction_inputs, true,
+DEFINE_bool(new_table_reader_for_compaction_inputs, true,
              "If true, uses a separate file handle for compaction inputs");
 
 DEFINE_int32(compaction_readahead_size, 0, "Compaction readahead size");