Summary:
We should validate this option, otherwise we may see
std::out_of_range thrown at: db/db_impl.cc:1124

1123     for (unsigned int i = 0; i <= end; i++) {
1124       std::string& to_delete = old_info_log_files.at(i);
1125       std::string full_path_to_delete =
1126           (immutable_db_options_.db_log_dir.empty()
Closes https://github.com/facebook/rocksdb/pull/1722

Differential Revision: D4379495

Pulled By: yiwu-arbug

fbshipit-source-id: e136552