expose-fs not getting forwarded

Nobody has claimed this yet.

I want to create a tutorial based on docker-browser-server and [command_line_bootcamp](https://github.com/blahah/command_line_bootcamp). My problem is that my filesystem seemingly does not get shown. Seems as if expose-fs is unable to connect.

I'm running docker-browser-server as a docker-container:
* From https://github.com/monsdar/bootcamp_docker-browser-server
* CMD: `CMD docker-browser-server monsdar/bootcamp-baseimage -p 8080`
* Run the container: `docker run -p 8080:8080 -v /var/run/docker.sock:/var/run/docker.sock monsdar/bootcamp-docker-browser-server`

My baseimage is from [here](https://github.com/monsdar/bootcamp_baseimage)
* It uses expose-fs
* It exposes port 8441

When connecting to docker-browser-server a new container gets created successfully (`Spawning new container (buj5ijhk4e)`), but this container does not map its internal port 8441 to the external port 8441. I guess this is why the frontend does not show any files. Docker maps 8441 to some random port though, which I can `curl localhost:12345` on and get the files and paths.

My testing frontend is here: https://monsdar.gitlab.io/bootcamp_test/?id=buj5ijhk4e, based on this repo: https://gitlab.com/monsdar/bootcamp_test

Any idea why this is happening? Is this a port-mapping issue, or am I looking in the wrong direction?

Reproduce the issue with the reported docker-browser-server command, the mounted Docker socket, and the bootcamp base image. Inspect how the spawned container's exposed port 8441 is forwarded and how expose-fs connects; compare the random mapped port with the frontend's expected endpoint. Done means the frontend can display the container's files through the documented setup.

Written by the indexing model from the issue text.