Describe: describe QOS for pods which dont have a QosClass property in status

[adietish]

related to #553

We currently only report QOS for pods which have a QosClass in their status (Pod.status.qosClass). If this is missing, we're reporting <none>.
A Qos can still be reported by looking at the containers and compute the findings though. kubectl does this with the following code:

https://github.com/kubernetes/kubectl/blob/b315eb8455a7d5c11ed788d1592b4afeca85771d/pkg/util/qos/qos.go#L45

// ComputePodQOS evaluates the list of containers to determine a pod's QoS class. This function is more
// expensive than GetPodQOS which should be used for pods having a non-empty .Status.QOSClass.
// A pod is besteffort if none of its containers have specified any requests or limits.
// A pod is guaranteed only when requests and limits are specified for all the containers and they are equal.
// A pod is burstable if limits and requests do not match across all containers.
func ComputePodQOS(pod *core.Pod) core.PodQOSClass {
	requests := core.ResourceList{}
	limits := core.ResourceList{}
	zeroQuantity := resource.MustParse("0")
	isGuaranteed := true
	// note, ephemeral containers are not considered for QoS as they cannot define resources
	allContainers := []core.Container{}
	allContainers = append(allContainers, pod.Spec.Containers...)
	allContainers = append(allContainers, pod.Spec.InitContainers...)
	for _, container := range allContainers {
		// process requests
		for name, quantity := range container.Resources.Requests {
			if !isSupportedQoSComputeResource(name) {
				continue
			}
			if quantity.Cmp(zeroQuantity) == 1 {
				delta := quantity.DeepCopy()
				if _, exists := requests[name]; !exists {
					requests[name] = delta
				} else {
					delta.Add(requests[name])
					requests[name] = delta
				}
			}
		}
		// process limits
		qosLimitsFound := sets.NewString()
		for name, quantity := range container.Resources.Limits {
			if !isSupportedQoSComputeResource(name) {
				continue
			}
			if quantity.Cmp(zeroQuantity) == 1 {
				qosLimitsFound.Insert(string(name))
				delta := quantity.DeepCopy()
				if _, exists := limits[name]; !exists {
					limits[name] = delta
				} else {
					delta.Add(limits[name])
					limits[name] = delta
				}
			}
		}

		if !qosLimitsFound.HasAll(string(core.ResourceMemory), string(core.ResourceCPU)) {
			isGuaranteed = false
		}
	}
	if len(requests) == 0 && len(limits) == 0 {
		return core.PodQOSBestEffort
	}
	// Check is requests match limits for all resources.
	if isGuaranteed {
		for name, req := range requests {
			if lim, exists := limits[name]; !exists || lim.Cmp(req) != 0 {
				isGuaranteed = false
				break
			}
		}
	}
	if isGuaranteed &&
		len(requests) == len(limits) {
		return core.PodQOSGuaranteed
	}
	return core.PodQOSBurstable
}