Automatic merge from submit-queue

move no k8s.io/kubernetes dependencies round 01

Builds on the previous, adds unit testing the staging dir.

moves

 1. pkg/healthz -> apiserver/pkg/healthz
 2. pkg/util/flushwriter -> apiserver/pkg/util/flushwriter
 3. pkg/auth/authenticator -> apiserver/pkg/authentication/authenticator
 4. pkg/auth/authorizer -> apiserver/pkg/authorization/authorizer

@sttts