Add the ability to turn off image pulling.

In v1beta3 proposal all of the mentioned ones (besides TCP/UDP) are now normalized to camelCase, with the sole exception being "kind" which we have an outstanding bug on.

----- Original Message -----
> > @@ -173,6 +173,16 @@ type LivenessProbe struct {
> >  	InitialDelaySeconds int64 `yaml:"initialDelaySeconds,omitempty"
> >  	json:"initialDelaySeconds,omitempty"`
> >  }
> >  
> > +// PullPolicy describes a policy for if/when to pull a container image
> > +type PullPolicy string
> > +
> > +const (
> > +	// Always attempt to pull the latest image
> > +	PullNewest PullPolicy = "PULL_NEWEST"
> 
> Clayton: which?  Protocol is an enum (though not enumerated in types.go,
> probably should be) and is caps.  RestartPolicy is a struct.  Kind is
> javaStyle.  CauseType is javaStyle.
> 
> We have a mish-mash.  I am biased to dislike javaStyle, but I'll run with it
> if that is the decision.
> 
> I nominate @bgrant0607 as decide on api-exposed string constants.  Unless the
> decision is "inconsistency is OK", we have some work to do to normalize.
> 
> ---
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> https://github.com/GoogleCloudPlatform/kubernetes/pull/1458/files#r18105018