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"
                },
...
```
port = port or config.PORT_CLOUDFORMATION
    backend_port = DEFAULT_PORT_CLOUDFORMATION_BACKEND
    print('Starting mock CloudFormation (%s port %s)...' % (get_service_protocol(), port))
    start_proxy_for_service('cloudformation', port, backend_port, update_listener)
    if RUN_SERVER_IN_PROCESS:
        cmd = 'python "%s" cloudformation -p %s -H 0.0.0.0' % (__file__, backend_port)
        env_vars = {'PYTHONPATH': ':'.join(sys.path)}
        return do_run(cmd, asynchronous, env_vars=env_vars)
    else:
        argv = ['cloudformation', '-p', str(backend_port), '-H', '0.0.0.0']
        thread = FuncThread(start_up, argv)
        thread.start()
        return thread
def set_moto_account_ids(resource_json):
    def fix_ids(obj, **kwargs):
        if isinstance(obj, dict):
            for key, value in obj.items():
                if isinstance(value, six.string_types):
                    if 'arn' in key.lower() or (':%s:' % TEST_AWS_ACCOUNT_ID) in value:
                        obj[key] = value.replace(TEST_AWS_ACCOUNT_ID, MOTO_ACCOUNT_ID)
        return obj
    return recurse_object(resource_json, fix_ids)
def get_entity_id(entity, resource_json=None):