imagePullPolicy missing enum for always, never, and IfNotPresent

[JPinkney]

Currently imagePullPolicy is just:

"imagePullPolicy": {
          "type": "string", 
          "description": "Image pull policy. One of Always, Never, IfNotPresent. Defaults to Always if :latest tag is specified, or IfNotPresent otherwise. Cannot be updated. More info: http://kubernetes.io/docs/user-guide/images#updating-images"
 }

But should have enum for always, never, and IfNotPresent