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"
                },
...
```
original_resource, new_resource_name, cloudformation_json, region_name):
        resource_name = cloudformation_json.get('Properties', {}).get('FunctionName') or new_resource_name
        return Lambda_create_from_cloudformation_json_orig(resource_name, cloudformation_json, region_name)
    if not hasattr(lambda_models.LambdaFunction, 'update_from_cloudformation_json'):
        lambda_models.LambdaFunction.update_from_cloudformation_json = Lambda_update_from_cloudformation_json
    
    def depl_delete_from_cloudformation_json(
            resource_name, resource_json, region_name):
        properties = resource_json['Properties']
        LOG.info('TODO: apigateway.Deployment.delete_from_cloudformation_json %s' % properties)
    if not hasattr(apigw_models.Deployment, 'delete_from_cloudformation_json'):
        apigw_models.Deployment.delete_from_cloudformation_json = depl_delete_from_cloudformation_json
    
    def vers_delete_from_cloudformation_json(
            resource_name, resource_json, region_name):
        properties = resource_json['Properties']
        LOG.info('TODO: apigateway.Deployment.delete_from_cloudformation_json %s' % properties)
    if not hasattr(lambda_models.LambdaVersion, 'delete_from_cloudformation_json'):
        lambda_models.LambdaVersion.delete_from_cloudformation_json = vers_delete_from_cloudformation_json
    
    @classmethod
    def RestAPI_create_from_cloudformation_json(cls, resource_name, cloudformation_json, region_name):