lib/plugins/aws/provider/awsProvider.js/AwsProvider/getServerlessDeploymentBucketName
class AwsProvider:  getServerlessDeploymentBucketName() {
    if (this.serverless.service.provider.deploymentBucket) {
      return BbPromise.resolve(this.serverless.service.provider.deploymentBucket);
    }
    return this.request('CloudFormation',
      'describeStackResource',
      {
        StackName: this.naming.getStackName(),
        LogicalResourceId: this.naming.getDeploymentBucketLogicalId(),
      }
    ).then((result) => result.StackResourceDetail.PhysicalResourceId);
  }