PLEG and kubelet race when reading and sending pod status to the apiserver.  PLEG
inserts status into a cache, and then signals kubelet.  Kubelet then eventually
reads the status out of that cache, but in the mean time the status could have
been changed by PLEG.

When a pod exits, pod status will no longer include the pod's IP address because
the network plugin/runtime will report "" for terminated pod IPs.  If this status
gets inserted into the PLEG cache before kubelet gets the status out of the cache,
kubelet will see a blank pod IP address.  This happens in about 1/5 of cases when
pods are short-lived, and somewhat less frequently for longer running pods.

To ensure consistency for properties of dead pods, copy an old status update's
IP address over to the new status update if (a) the new status update's IP is
missing and (b) all sandboxes of the pod are dead/not-ready (eg, no possibility
for a valid IP from the sandbox).

Fixes: https://github.com/kubernetes/kubernetes/issues/47265