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. 
def sub(match):
            
            bucket_name = normalize_bucket_name(match.group(1))
            return '/%s%s' % (bucket_name, match.group(2) or '')
        path_new = re.sub(r'/([^?/]+)([?/].*)?', sub, path)
        if path == path_new:
            return
        url = 'http://%s:%s%s' % (constants.LOCALHOST, constants.DEFAULT_PORT_S3_BACKEND, path_new)
        return url
    def return_response(self, method, path, data, headers, response):
        path = to_str(path)
        method = to_str(method)
        bucket_name = get_bucket_name(path, headers)
        
        persistence.record('s3', method, path, data, headers, response=response)
        
        hostname_parts = headers['host'].split('.')
        if (not bucket_name or len(bucket_name) == 0) and len(hostname_parts) > 1:
            bucket_name = hostname_parts[0]
        
        
        
        key = None
        if method == 'POST':