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.
When this function is updated please also update staging/src/k8s.io/kubectl/pkg/util/qos/qos.go
GetPodQOS returns the QoS class of a pod persisted in the PodStatus.QOSClass field.
If PodStatus.QOSClass is empty, it returns value of ComputePodQOS() which evaluates pod's QoS class.