db_bench to by default verify checksum

Summary: Closes https://github.com/facebook/rocksdb/pull/2575

Differential Revision: D5417350

Pulled By: siying

fbshipit-source-id: 4bc11e35a7256167a5a7d2f586f2ac74c0deddb0

tools/db_bench_tool.cc

@@ -489,7 +489,7 @@ static bool ValidateCacheNumshardbits(const char* flagname, int32_t value) {
   return true;
 }
 
-DEFINE_bool(verify_checksum, false, "Verify checksum for every block read"
+DEFINE_bool(verify_checksum, true, "Verify checksum for every block read"
             " from storage");
 
 DEFINE_bool(statistics, false, "Database statistics");