Upgraded from 99c19923, branch release-3.0.

This required fetching or upgrading the following:
* k8s.io/api to kubernetes-1.9.1
* k8s.io/apimachinery to kubernetes-1.9.1
* github.com/juju/ratelimit to 1.0.1
* github.com/spf13/pflag to 4c012f6d

Also, update Scope's imports/function calls to be compatible with the new client.