Based on the description in commit 63ef557 this was added so that the
migrate command does not move the pause process into a separate cgroup.

It should however not disable the rejoining of the userns when the pause
process join failed. BEcause of this we end up calling migrate without a
userns and that then can fail if there are actual contianer it tries to
cleanup.

Fixes: 63ef557 ("command: migrate doesn't move process to cgroup")

Signed-off-by: Paul Holzinger <[email protected]>

Just a minor improvement as we know the size needed for the slice we can
allocate it only once instead of the append having to resize it.

Signed-off-by: Paul Holzinger <[email protected]>

When trying to join the conmon pid to recreate the pause process based
on the namespace it can be that the pid is no longer valid, i.e. when
conmon crashed or was killed.

Currently we have a big issue that can be reproduced using:
$ podman run -d quay.io/libpod/testimage:20241011 sleep 100
$ killall -9 conmon
$ killall catatonit

All commands would fail as we keep trying to rejoin the namespace of the
non existing conmon process.

So to address that fall back to creating a new namespace if we fail to
join the conmon pids.

Signed-off-by: Paul Holzinger <[email protected]>

There doesn't seem any reason why the system commands should not join
the userns. In particular the main commands use ParentNSRequired and
UnshareNSRequired when they don't want to be joined to the main userns.
Since the system command don't set these the go code does the join and
re-exec anyway so might as well use the shortcut to speed that up.

Signed-off-by: Paul Holzinger <[email protected]>