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"
                },
...
```
resource_map = self.resource_map
            for i in range(MAX_DEPENDENCY_DEPTH):
                unresolved = getattr(resource_map, '_unresolved_resources', {})
                if not unresolved:
                    set_status('CREATE_COMPLETE')
                    return resource_map
                resource_map._unresolved_resources = {}
                for resource_id, resource_details in unresolved.items():
                    
                    parse_and_create_resource(*resource_details, force_create=True)
                if unresolved.keys() == resource_map._unresolved_resources.keys():
                    
                    LOG.warning('Unresolvable dependencies, there may be undeployed stack resources: %s' % unresolved)
                    break
            set_status('CREATE_FAILED')
            raise Exception('Unable to resolve all CloudFormation resources after traversing ' +
                'dependency tree (maximum depth %s reached)' % MAX_DEPENDENCY_DEPTH)
        
        FuncThread(run_loop).start()
    FakeStack.initialize_resources = initialize_resources
def inject_stats_endpoint():
    """ Inject a simple /_stats endpoint into the moto server backend Web app. """
    
    from moto import server as moto_server
    def _get_stats():