lib/plugins/aws/provider/awsProvider.js/AwsProvider/getApiGatewayRestApiId
class AwsProvider:  getApiGatewayRestApiId() {
    if (this.serverless.service.provider.apiGateway
      && this.serverless.service.provider.apiGateway.restApiId) {
      return this.serverless.service.provider.apiGateway.restApiId;
    }

    return { Ref: this.naming.getRestApiLogicalId() };
  }