Refactor --root option

Since version 2 docker allow to connect as root using
```
docker-compose --user=root
```

Odoo image is root by default and it's switch with gosu so in that case the option --user=root is useless, but the images without gosu can be used with the option --user=root


So we need to make the docky run / exec compatible with this kind of image out-of-box

