changeMode(mode) {
		let promise;
		if(mode === 'idle') {
			return this.setPower(false);
		} else {
			if(this.power()) {
				// Already powered on, do nothing
				promise = Promise.resolve();
			} else {
				// Not powered on, power on
				promise = this.setPower(true);
			}
		}

		return promise.then(() => {
			return this.call('set_mode', [ mode ], {
				refresh: [ 'power', 'mode' ],
				refreshDelay: 200
			})
				.then(MiioApi.checkOk)
				.catch(err => {
					throw err.code === -5001 ? new Error('Mode `' + mode + '` not supported') : err;
				});
		});
	}
Set the mode of this device.