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);
  }