Refactor PodStatus to PodCondition in internal API for v1beta3

Change PodStatus (string) to PodCondition (string) to make space for new PodStatus (struct) in v1beta3 API.

Change the constant values for Pod statuses to match v1beta3 API.
// PodSucceeded means that all containers in the pod have voluntarily terminated with a container exit code of 0, and the system is not going to restart any of these containers.