Hi!

I have noticed that today (25th of Feb) a new version of localstack docker image was pushed to the repository (82c83ff027114060938856eac5dc7be1d534afd0b7711510246de4a76dde2396) and this version fails in my integration tests with an exception:

```
2020-02-25T12:09:44:ERROR:localstack.services.generic_proxy: Error forwarding request: An error occurred (404) when calling the HeadObject operation: Not Found Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/generic_proxy.py", line 303, in forward updated_response = self.proxy.update_listener.return_response(**kwargs)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 954, in return_response
send_notifications(method, bucket_name, object_path, version_id)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 178, in send_notifications
send_notification_for_subscriber(notif, bucket_name, object_path,
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 191, in send_notification_for_subscriber
object_size = s3_client.head_object(Bucket=bucket_name, Key=key).get('ContentLength', 0)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 316, in _api_call
return self._make_api_call(operation_name, kwargs)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 626, in _make_api_call
  raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (404) when calling the HeadObject operation: Not Found
```
The same setup in docker-compose works with version 0.10.7 and 0.10.6 without any errors or exceptions. 
return
    s3_client = aws_stack.connect_to_service('s3')
    key = urlparse.urlparse(object_path[1:]).path
    object_size = s3_client.head_object(Bucket=bucket_name, Key=key).get('ContentLength', 0)
    
    message = get_event_message(
        event_name=event_name,
        bucket_name=bucket_name,
        file_name=key,
        file_size=object_size,
        version_id=version_id
    )
    message = json.dumps(message)
    if notif.get('Queue'):
        sqs_client = aws_stack.connect_to_service('sqs')
        try:
            queue_url = queue_url_for_arn(notif['Queue'])
            sqs_client.send_message(QueueUrl=queue_url, MessageBody=message)
        except Exception as e:
            LOGGER.warning('Unable to send notification for S3 bucket "%s" to SQS queue "%s": %s' %
                (bucket_name, notif['Queue'], e))
    if notif.get('Topic'):
        sns_client = aws_stack.connect_to_service('sns')
        try:
            sns_client.publish(TopicArn=notif['Topic'], Message=message, Subject='Amazon S3 Notification')
        except Exception:
            LOGGER.warning('Unable to send notification for S3 bucket "%s" to SNS topic "%s".' %
                (bucket_name, notif['Topic']))
    
    lambda_function_config = notif.get('CloudFunction') or notif.get('LambdaFunction')