FFmpegfs no longer detects Docker

[nschlia]

FMmpegfs no longer detects that it is running under Docker, reason see https://stackoverflow.com/questions/69002675/on-debian-11-bullseye-proc-self-cgroup-inside-a-docker-container-does-not-sho (thanks to @igor-epam for providing the link).

Probably until Debian is updated, there should be a different way to disable the mount check. Currently it is always done, unless a Docker container is detected. Because the check fails, FFmpegfs refuses to start.

A new command line parameter would help: --nomountcheck

If present, no check is done, and the binary will start.

Also see issue #79

[nschlia]

Here's a quick solution:
https://stackoverflow.com/questions/68816329/how-to-get-docker-container-id-from-within-the-container-with-cgroup-v2
Add --cgroupns host to the run command.