Add the ability to turn off image pulling.

He's the decider

----- 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"
> 
> Any disagreement on @bgrant0607 deciding?  I'd be fine to change these new
> ones and TCP/UDP to tcp/udp (matches docker better anyway) - we already
> ignore case on input.  Brian has reasonable taste, I'll be bound by his
> decision, which we will write down in the API conventions doc, if it is not
> there already.
> 
> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/GoogleCloudPlatform/kubernetes/pull/1458/files#r18105841