计算沙箱与容器的变化

该阶段主要检测沙箱容器（pause）与其他容器（初始化容器、临时容器、常规容器）的变化，也就是pod期望运行状态与实际运行状态。

当对pod的操作为创建时，显然不存在实际运行状态。

podActions是一个记录pod期望运行状态与实际运行状态的对象

当新建pod时，以下字段取值如下：

• KillPod: 是否停止pod所有容器（pause容器、初始化容器、临时容器、常规容器），该值为true
• CreateSandbox: 是否创建沙箱，该值为true
• Attempt: 尝试创建pod沙箱次数，该值为0、
• ContainersToStart: 一般容器数组，，该值对应pod的spec.containers[x]数组
• NextInitContainerToStart: 下一个将启动的初始化容器，该值对应pod的spec.initContainers[0]

// podActions keeps information what to do for a pod.
type podActions struct {
    // Stop all running (regular, init and ephemeral) containers and the sandbox for the pod.
    KillPod bool
    // Whether need to create a new sandbox. If needed to kill pod and create
    // a new pod sandbox, all init containers need to be purged (i.e., removed).
    CreateSandbox bool
    // The id of existing sandbox. It is used for starting containers in ContainersToStart.
    SandboxID string
    // The attempt number of creating sandboxes for the pod.
    Attempt uint32

    // The next init container to start.
    NextInitContainerToStart *v1.Container
    // ContainersToStart keeps a list of indexes for the containers to start,
    // where the index is the index of the specific container in the pod spec (
    // pod.Spec.Containers.
    ContainersToStart []int
    // ContainersToKill keeps a map of containers that need to be killed, note that
    // the key is the container ID of the container, while
    // the value contains necessary information to kill a container.
    ContainersToKill map[kubecontainer.ContainerID]containerToKillInfo
    // EphemeralContainersToStart is a list of indexes for the ephemeral containers to start,
    // where the index is the index of the specific container in pod.Spec.EphemeralContainers.
    EphemeralContainersToStart []int
}