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"
                },
...
```
elif isinstance(resource, apigw_models.Resource):
            api_id = props['RestApiId']
            backend.apis[api_id].resources.pop(resource.id, None)
            backend.apis[api_id].resources[new_id] = resource
            resource.id = new_id
        elif isinstance(resource, apigw_models.Deployment):
            api_id = props['RestApiId']
            backend.apis[api_id].deployments.pop(resource['id'], None)
            backend.apis[api_id].deployments[new_id] = resource
            resource['id'] = new_id
        else:
            LOG.warning('Unexpected resource type when updating ID: %s' % type(resource))
    parse_and_create_resource_orig = parsing.parse_and_create_resource
    parsing.parse_and_create_resource = parse_and_create_resource
    parse_and_update_resource_orig = parsing.parse_and_update_resource
    parsing.parse_and_update_resource = parse_and_update_resource
    
    def parse_output(output_logical_id, output_json, resources_map):
        try:
            return parse_output_orig(output_logical_id, output_json, resources_map)
        except KeyError:
            output = Output()
            output.key = output_logical_id
            output.value = None
            output.description = output_json.get('Description')
            return output
    parse_output_orig = parsing.parse_output
    parsing.parse_output = parse_output
    
    def DynamoDB_Table_get_cfn_attribute(self, attribute_name):