cri_stats_provider: overload nil as 0 for exited containers stats

Always report 0 cpu/memory usage for exited containers to make
metrics-server work as expect.

Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>

pkg/kubelet/stats/helper.go

@@ -326,3 +326,7 @@ func getUint64Value(value *uint64) uint64 {
 
 	return *value
 }
+
+func Uint64Ptr(i uint64) *uint64 {
+	return &i
+}