function checkStatus (uri, resp) {
	const {statusCode, body: {error}} = resp
	assert.equal(statusCode, 200, `error status code ${uri}: ${error}`)
}
ensure that the registry responded with an accepted HTTP status code
(`200`).
@param  {String} uri - URI used for retrieving the supplied response.
@param  {Number} resp - HTTP response object.
@throws {assert.AssertionError} if the status code is not 200.