Add RestartPolicy to Pod and PodTemplate

This is the first PR to add RestartPolicy to Pod. Next PRs will hook policy with kubelets. 
I do not like that the errorList type added this Append method. It breaks the ordinary go idiom of ```x = append(x, blah)```. Recommend using []error and that method of append, and then you can also get rid of the cast Brendan is complaining about below.