This fixes the race that happens in rktnetes when pod B invokes
'kubenet.SetUpPod()' before another pod A becomes actually running.
The second 'kubenet.SetUpPod()' call will not pick up the pod A
and thus overwrite the host port iptable rules that breaks pod A.
This PR fixes the case by listing all 'active pods' (all non-exited
pods) instead of only running pods.
Because rkt pod runs after plugin.SetUpPod() is called, so
getRunningPods() does not return the newly created pod, which
causes the hostport iptable rules to be missing for this new pod.
