function onError( error ) {
		debug( 'Error encountered while querying endpoint: %s', error.message );
		if ( error instanceof Error ) {
			err = {
				'status': 500,
				'message': 'Request error: ' + error.message
			};
			return clbk( err );
		}
		return clbk( error, res, body );
	}
Event listener invoked after encountering an error.

@private
@param {Error} error - error object
@returns {void}