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"
                },
...
```
cloudformation = aws_stack.connect_to_service('cloudformation')
        invalid_json = '{"this is invalid JSON"="bobbins"}'
        try:
            cloudformation.validate_template(TemplateBody=invalid_json)
            self.fail('Should raise ValidationError')
        except (ClientError, ResponseParserError) as err:
            if isinstance(err, ClientError):
                self.assertEqual(err.response['ResponseMetadata']['HTTPStatusCode'], 400)
                self.assertEqual(err.response['Error']['Message'], 'Template Validation Error')
    def test_list_stack_resources_returns_queue_urls(self):
        cloudformation = aws_stack.connect_to_resource('cloudformation')
        template = template_deployer.template_to_json(load_file(TEST_TEMPLATE_2))
        stack_name = 'stack-%s' % short_uid()
        cloudformation.create_stack(StackName=stack_name, TemplateBody=template)
        def check_stack():
            stack = get_stack_details(stack_name)
            self.assertEqual(stack['StackStatus'], 'CREATE_COMPLETE')
        retry(check_stack, retries=3, sleep=2)
        stack_summaries = list_stack_resources(stack_name)
        queue_urls = get_queue_urls()
        topic_arns = get_topic_arns()
        stack_queues = [r for r in stack_summaries if r['ResourceType'] == 'AWS::SQS::Queue']
        for resource in stack_queues:
            self.assertIn(resource['PhysicalResourceId'], queue_urls)
        stack_topics = [r for r in stack_summaries if r['ResourceType'] == 'AWS::SNS::Topic']
        for resource in stack_topics:
            self.assertIn(resource['PhysicalResourceId'], topic_arns)
    def test_create_change_set(self):