Automatic merge from submit-queue (batch tested with PRs 40505, 34664, 37036, 40726, 41595)
dockertools: call TearDownPod when GC-ing infra pods
The docker runtime doesn't tear down networking when GC-ing pods.
rkt already does so make docker do it too. To ensure this happens,
infra pods are now always GC-ed rather than gating them by
containersToKeep.
This prevents IPAM from leaking when the pod gets killed for
some reason outside kubelet (like docker restart) or when pods
are killed while kubelet isn't running.
Fixes: https://github.com/kubernetes/kubernetes/issues/14940
Related: https://github.com/kubernetes/kubernetes/pull/35572