Kubelet talks securely to apiserver.

Configure apiserver to serve Securely on port 6443.
Generate token for kubelets during master VM startup.
Put token into file apiserver can get and another file the kubelets can get.
Added e2e test.
Don't reference non-existent token file if not GCE.
Only test events on GCE.
Merge pull request #2387 from erictune/secure_port_on

Kubelet talks securely to apiserver