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. 
key, redirect_url = multipart_content.find_multipart_key_value(data, headers)
            if key and redirect_url:
                response.status_code = 303
                response.headers['Location'] = expand_redirect_url(redirect_url, key, bucket_name)
                LOGGER.debug('S3 POST {} to {}'.format(response.status_code, response.headers['Location']))
            key, status_code = multipart_content.find_multipart_key_value(
                data, headers, 'success_action_status')
            if response.status_code == 200 and status_code == '201' and key:
                response.status_code = 201
                response._content = self.get_201_reponse(key, bucket_name)
                response.headers['Content-Length'] = str(len(response._content))
                response.headers['Content-Type'] = 'application/xml; charset=utf-8'
                return response
        parsed = urlparse.urlparse(path)
        bucket_name_in_host = headers['host'].startswith(bucket_name)
        should_send_notifications = all([
            method in ('PUT', 'POST', 'DELETE'),
            '/' in path[1:] or bucket_name_in_host,
            
            
            bucket_name_in_host or (len(path[1:].split('/')) > 1 and len(path[1:].split('/')[1]) > 0),
            self.is_query_allowable(method, parsed.query)
        ])
        
        if should_send_notifications:
            
            if key:
                object_path = '/' + key
            elif bucket_name_in_host:
                object_path = parsed.path