function saveConnections(config, callback) {
  // only save "connections" part, nothing else from config object
  let saveCfg = {
    connections: config.util.toObject(config.connections).map(function(c) {
      delete c.connectionId;
      return c;
    })
  };
  fs.writeFile(getConfigPath('connections'), JSON.stringify(saveCfg, null, 2), function (err) {
    if (typeof callback === 'function') callback(err ? err : null);
  });
}
Helper to save all current connections defined inside config object into
 configuration file for connections

 @see getConfigPath
 @param {object} config - config object to save configurations from
 @param {function} callback - callback after save, error object as first param on failure