function startServer(options, callback) {
	const server = new TestServer(options);
	if (callback) {
		return server.start(callback)
	}
	return new Promise((resolve, reject) => {
		server.start((error, result) => {
			if (error) return reject(error)
			return resolve(result)
		})
	})
}
Start a test server. Parameters:
- `options`, can contain:
	 - port: the port to use, default 7357.
	 - delay: wait the given milliseconds before answering.
	 - quiet: do not log any messages.
	 - percent: give an error (default 500) on some % of requests.
	 - error: set an HTTP error code, default is 500.
	 - logger: function to log all incoming requests.
	 - body: to return in requests.
	 - file: to read and return as body.
- `callback`: optional callback, called after the server has started.
  If not present will return a promise.