Instalog & Testlog tries to call tempfile.mkstemp directory to prevent dependency on file_utils, but that creates more potential leaks, or improper usage.

For example: (py/instalog/plugins/input_rpc.py)

        fd, tmp_path = tempfile.mkstemp(dir=self._tmp_dir)
        # If anything in the 'try' block raises an exception, make sure we
        # close the file handle created by mkstemp.
        try:
          with open(tmp_path, 'w') as f:
            f.write(zlib.decompress(base64.b64decode(att_data['value'])))
        finally:
          os.close(fd)

When fd is still open, we should open do another open(w). This may cause unexpected result on some platforms.

py/instalog/plugins/input_http.py:

    fd, tmp_path = tempfile.mkstemp(prefix=data.name + '_', dir=self._tmp_dir)
    with os.fdopen(fd, 'w') as f:
      if data.file:
        shutil.copyfileobj(data.file, f)
      # cgi.MiniFieldStorage does not have attribute 'file', since it stores
      # the binary data in-memory.
      else:
        f.write(data.value)

fd may keep open if fdopen raises exception (although for most of the case, this is unlikely to happen)

In fact, there are three styles of using mkstemp in Instalog:
 1. fd, path = mkstemp(); os.close(fd) with open(path)....
 2. fd, path = mkstemp(); try: with open(...) finally: os.close(fd)
 3. fd, path = mkstemp(); with os.fdopen(...)

I think we should probably always use same style, with some simple way to check.

What about always using tempfile.NamedTemporaryFile(delete=True/False) ?