v2: do not parse io.stat as KV stat
v2: do not parse io.stat as KV stat

Only `cpu.stat` and `memory.stat` should be treated as KV stat file.

Fix https://github.com/containerd/containerd/issues/3951

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

containerd/cgroups