Given a CF template that defines outputs as named exports, I expect the "describe-stack" endpoint to include the exported names. With localstack, that is currently not the case.

Example template:
```yaml
  Outputs:
    VPCId:
      Value: {Ref: MyVPC}
      Export:
        Name: My-VPCId

  Resources:
    MyVPC:
      Properties:
        CidrBlock: 10.0.0.0/16
      Type: AWS::EC2::VPC

```

AWS:
```
$ aws cloudformation describe-stacks
...
                {
                    "OutputKey": "VPCId",
                    "OutputValue": "vpc-0123456789",
                    "ExportName": "My-VPCId"
                },

```

localstack:
```
$ aws cloudformation --endpoint-url=http://localhost:4581/ describe-stacks
...
                {
                    "OutputKey": "VPCId",
                    "OutputValue": "vpc-0123456789"
                },
...
```
if attribute_name in ['Arn', 'QueueArn']:
            return aws_stack.sqs_queue_arn(queue_name=self.name)
        return SQS_Queue_get_cfn_attribute_orig(self, attribute_name)
    SQS_Queue_get_cfn_attribute_orig = sqs_models.Queue.get_cfn_attribute
    sqs_models.Queue.get_cfn_attribute = SQS_Queue_get_cfn_attribute
    
    def S3_Bucket_get_cfn_attribute(self, attribute_name):
        if attribute_name in ['Arn']:
            return aws_stack.s3_bucket_arn(self.name)
        return S3_Bucket_get_cfn_attribute_orig(self, attribute_name)
    S3_Bucket_get_cfn_attribute_orig = s3_models.FakeBucket.get_cfn_attribute
    s3_models.FakeBucket.get_cfn_attribute = S3_Bucket_get_cfn_attribute
    
    @property
    def SQS_Queue_physical_resource_id(self):
        result = SQS_Queue_physical_resource_id_orig.fget(self)
        if '://' not in result:
            
            return aws_stack.get_sqs_queue_url(result)
        return result
    SQS_Queue_physical_resource_id_orig = sqs_models.Queue.physical_resource_id
    sqs_models.Queue.physical_resource_id = SQS_Queue_physical_resource_id
    
    def LogGroup_get_cfn_attribute(self, attribute_name):