Arender on docker-compose

It was impossible to run Arender's features in a docker compose environment described here
https://github.com/nuxeo-sandbox/mle-demos/blob/master/2019/test12/docker-compose.yml#L47

Step to reproduce:

1. clone repo
2. edit your /etc/hosts to map arender to localhost
3. cd 2019/test12
4. launch.sh
5. and open http://localhost:8103 to try Arender on one asset (KO)

Test done but still KO:

mapping nuxeo.url, and mapping networks from docker to localhost like done here
https://github.com/nuxeo/nuxeo-tools-docker-priv/tree/master/arender

and finally here
https://github.com/nuxeo-sandbox/mle-demos/blob/master/2019/test16/docker-compose.yml#L10

the Arender's demo is working BUT all links (like notifications) sent by Nuxeo are with a wrong url (due to wrong nuxeo.url).