Make current_container_facts work with newer Docker versions and latest ansible-test container changes

[felixfontein]

SUMMARY

It does seem to no longer work, might be related to ansible/ansible#78550.

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

current_container_facts

[github-actions]

Docs Build 📝

Thank you for contribution!✨

This PR has been merged and the docs are now incorporated into main:
https://ansible-collections.github.io/community.docker/branch/main

[felixfontein]

CC @mattclay, looking at /proc/self/cpuset to figure out the current container breaks down on newer Docker daemons, and also no longer works with the alpine3 container on AZP in ansible-test since ansible/ansible#78550 was merged (don't ask me why only for that one...). I did some trying around, and looking at /proc/self/mountinfo and searching for /etc/hostname seems to work pretty well as a quick replacement (though that assumes that the user didn't change their docker data directory to something else than /var/lib/docker/ - or maybe this is also a fixed string that isn't related to the position of that directory on the host system?). This might be useful for https://github.com/ansible/ansible/blob/devel/test/lib/ansible_test/_internal/docker_util.py#L576.

[kristianheljas]

Other than the outdated comment and test with docker, look good. Podman worked flawlessly

[mattclay]

@felixfontein Looking at /proc/self/cpuset is unreliable because of cgroup namespaces. It contains a host-specific path only when the host namespace is used:

$ docker run -it --rm --cgroupns host quay.io/bedrock/alpine:3.17.0 cat /proc/self/cpuset
/docker/a34f76a8f390f33188505c9be17734fcd41d6b1afc014bb36ad0b030a24ffe11
$ docker run -it --rm --cgroupns private quay.io/bedrock/alpine:3.17.0 cat /proc/self/cpuset
/

[felixfontein]

@kristianheljas @mattclay thanks for testing, reviewing, and commenting!

[felixfontein]

Manual backport of bugfix part to stable-2 in #512.