Currently, kubelet silently ignores pods that caused host port conflict. This
commit surfaces the error by recording an event.
It also makes sure that kubelet iterates through the pods in the order of the
creation timestamp, which ensures that pods created later are ignored on
conflict.
Because time.Time doesn't work correctly with our YAML package, it is necessary
to introduce a type, util.Time, which serializes correctly to JSON and YAML.
Eventually we would like timestamping to cut across storage implementations;
for now, we set it in each storage.