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. 
if headers.get(CONTENT_SHA256_HEADER) == STREAMING_HMAC_PAYLOAD:
            modified_data = strip_chunk_signatures(modified_data or data)
            headers['content-length'] = headers.get('x-amz-decoded-content-length')
        
        
        if method == 'POST':
            original_data = modified_data or data
            expanded_data = multipart_content.expand_multipart_filename(original_data, headers)
            if expanded_data is not original_data:
                modified_data = expanded_data
        
        
        if method == 'PUT' and not headers.get('content-type'):
            headers['content-type'] = 'binary/octet-stream'
        
        query = parsed_path.query
        path = parsed_path.path
        bucket = path.split('/')[1]
        query_map = urlparse.parse_qs(query, keep_blank_values=True)
        
        append_metadata_headers(method, query_map, headers)
        
        headers_changed = fix_metadata_key_underscores(request_headers=headers)
        if query == 'notification' or 'notification' in query_map:
            
            response = handle_notification_request(bucket, method, data)
            return response
        if query == 'cors' or 'cors' in query_map: