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"
                },
...
```
def fix_ids(obj, **kwargs):
        if isinstance(obj, dict):
            obj = dict(obj)
            for key, value in obj.items():
                if isinstance(value, BaseModel):
                    entity_id = get_entity_id(value)
                    obj[key] = entity_id or value
        return obj
    return recurse_object(resource_json, fix_ids)
def update_physical_resource_id(resource):
    phys_res_id = getattr(resource, 'physical_resource_id', None)
    if not phys_res_id:
        if isinstance(resource, lambda_models.LambdaFunction):
            func_arn = aws_stack.lambda_function_arn(resource.function_name)
            resource.function_arn = resource.physical_resource_id = func_arn
        elif isinstance(resource, sfn_models.StateMachine):
            sm_arn = aws_stack.state_machine_arn(resource.name)
            resource.physical_resource_id = sm_arn
        elif isinstance(resource, service_models.StepFunctionsActivity):
            act_arn = aws_stack.stepfunctions_activity_arn(resource.params.get('Name'))
            resource.physical_resource_id = act_arn
        elif isinstance(resource, kinesis_models.Stream):
            resource.physical_resource_id = resource.stream_name
        else:
            LOG.warning('Unable to determine physical_resource_id for resource %s' % type(resource))
def apply_patches():
    """ Apply patches to make LocalStack seamlessly interact with the moto backend.
        TODO: Eventually, these patches should be contributed to the upstream repo! """
    
    def get_key(self, bucket_name, key_name, version_id=None):