def validate_driver_config!(driver_config)
      raise_argument_error!(:host)        unless driver_config.has_key? :host
      raise_argument_error!(:port)        unless driver_config.has_key? :port
      raise_argument_error!(:namespace)   unless driver_config.has_key? :namespace
      raise_argument_error!(:timeout_sec) unless driver_config.has_key? :timeout_sec
      raise_argument_error!(:pool_size)   unless driver_config.has_key? :pool_size

      driver_config[:config_key] = :none  unless driver_config.has_key? :config_key

      return driver_config
    end
def validate_driver_config!(driver_config)
      raise_argument_error!(:host)        unless driver_config.has_key? :host
      raise_argument_error!(:port)        unless driver_config.has_key? :port
      raise_argument_error!(:namespace)   unless driver_config.has_key? :namespace
      raise_argument_error!(:timeout_sec) unless driver_config.has_key? :timeout_sec
      raise_argument_error!(:pool_size)   unless driver_config.has_key? :pool_size

      driver_config[:config_key] = :none  unless driver_config.has_key? :config_key

      return driver_config
    end
Validate driver_config.
 This method raise ArgumentError, if missing driver_config.

 @param driver_config [Hash] driver config.
 @return [Hash] driver_config