function readConfigFileContent (configPath) {

  let rawBufContent = fs.readFileSync(configPath);

  if (!isUTF8(rawBufContent)) {
    throw new Error(`The config file at "${configPath}" contains invalid charset, expect utf8`);
  }

  return stripBom(rawBufContent.toString("utf8"));
}
Read proper content from config file.
If the chartset of the config file is not utf-8, one error will be thrown.
@param {String} configPath
@return {String}