Automatic merge from submit-queue

Disable readyReplicas validation for Deployments

Because there is no field in 1.5, when we update to 1.6 and the
controller tries to update the Deployment, it will be denied by
validation because the pre-existing availableReplicas field is greater
than readyReplicas (normally readyReplicas should always be greater or
equal).

Fixes https://github.com/kubernetes/kubernetes/issues/43392

@kubernetes/sig-apps-bugs