Currently, if a nested container wants to share the pid namespace of its parent container, we allow the framework to set `LinuxInfo.share_pid_namespace`.
If the nested container does not have its own rootfs (i.e., using the host rootfs), the `/proc` is not re-mounted:
This is problematic because the nested container will fork host's mount namespace, thus inherit the `/proc` there. As a result, `/proc/<pid>` are still for the host pid namespace. The pid namespace of the parent container might be different than that of the host pid namspace.
As a result, `ps aux` in the nested container will show all process information on the host pid namespace. Although, the pid namespace of the nested container is different than that of the host.