[Improvement] support the path without scheme prefix when invoke gvfs api

[coolderli]

What would you like to be improved?

Some engines like Tensorflow may create the GravitinoVirtualFilesystem, and pass the path that does not have the scheme prefix.
In the current implementation, the path has to set the scheme prefix, it will not work with TensorFlow. In the issue, we will improve it.

Tensorflow will parseHadoopPath after creating the HadoopFileSystem(GravitinoVirtualFIleSystem). After that, it will use the path that has no scheme prefix to invoke API.

void ParseHadoopPath(const std::string& fname, std::string* scheme,
                     std::string* namenode, std::string* path) {
  size_t scheme_end = fname.find("://") + 2;
  // We don't want `://` in scheme.
  *scheme = fname.substr(0, scheme_end - 2);
  size_t nn_end = fname.find("/", scheme_end + 1);
  if (nn_end == std::string::npos) {
    *namenode = fname.substr(scheme_end + 1);
    *path = "";
    return;
  }
  *namenode = fname.substr(scheme_end + 1, nn_end - scheme_end - 1);
  // We keep `/` in path.
  *path = fname.substr(nn_end);  // here, truncate the scheme prefix
}

 ParseHadoopPath(path, &scheme, &namenode, &hdfs_path);

  auto handle = libhdfs->hdfsOpenFile(fs, hdfs_path.c_str(), O_WRONLY, 0, 0, 0);   // here. the hdfs_path has no gvfs:// prefix

How should we improve?

improve the compatibility to support the path with scheme prefix and the path without scheme prefix