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. 
pass
        if response:
            reset_content_length = False
            
            append_cors_headers(bucket_name, request_method=method, request_headers=headers, response=response)
            append_last_modified_headers(response=response)
            append_list_objects_marker(method, path, data, response)
            fix_location_constraint(response)
            fix_range_content_type(bucket_name, path, headers, response)
            fix_delete_objects_response(bucket_name, method, parsed, data, headers, response)
            fix_metadata_key_underscores(response=response)
            fix_creation_date(method, path, response=response)
            fix_etag_for_multipart(data, headers, response)
            
            
            if method == 'PUT' and ('X-Amz-Security-Token=' in path or
                    'X-Amz-Credential=' in path or 'AWSAccessKeyId=' in path):
                response._content = ''
                reset_content_length = True
            response_content_str = None
            try:
                response_content_str = to_str(response._content)
            except Exception:
                pass
            
            
            if method == 'GET':
                query_map = urlparse.parse_qs(parsed.query, keep_blank_values=True)
                for param_name, header_name in ALLOWED_HEADER_OVERRIDES.items():
                    if param_name in query_map: