Error when using PDB with Sandbox

[barney-s]

Warning seen in pdb events:

Warning  CalculateExpectedPodCountFailed  19s (x6 over 15m)  controllermanager  
Failed to calculate the number of expected pods: 
Internal error occurred: the spec replicas field ".spec.replicas" does not exist

Reason:
Sandbox implements scale .spec.replicas as an int pointer.
when it is not specified, the controller defaults locally to 1.
It does not set the value 1 in the resource.

Then when PDB tries to use scale subresource Get() https://github.com/kubernetes/kubernetes/blob/2711e8cb53987ad7aca9eee21e1be3a4961fea39/pkg/controller/disruption/disruption.go#L387

Scale get reads fails at read from etcd/crd: https://github.com/kubernetes/kubernetes/blob/2711e8cb53987ad7aca9eee21e1be3a4961fea39/staging/src/k8s.io/apiextensions-apiserver/pkg/registry/customresource/etcd.go#L183

scale subresource get fails when replica is not specified.

Options to fix:

1. make .spec.replicas an int instead of *int (how does defaulting to 1 work in this case ?)
2. default in controller and write back to the sandbox object (breaks controller mutating spec principle)

Related PR #85