Update Kubernetes from v1.11.3 to v1.12.1

* Mount an empty dir for the controller-manager to work around
https://github.com/kubernetes/kubernetes/issues/68973
* Update coreos/pod-checkpointer to strip affinity from
checkpointed pod manifests. Kubernetes v1.12.0-rc.1 introduced
a default affinity that appears on checkpointed manifests; but
it prevented scheduling and checkpointed pods should not have an
affinity, they're run directly by the Kubelet on the local node
* https://github.com/kubernetes-incubator/bootkube/issues/1001
* https://github.com/kubernetes/kubernetes/pull/68173

aws/container-linux/kubernetes/cl/controller.yaml.tmpl

@@ -122,7 +122,7 @@ storage:
       contents:
         inline: |
           KUBELET_IMAGE_URL=docker://k8s.gcr.io/hyperkube
-          KUBELET_IMAGE_TAG=v1.11.3
+          KUBELET_IMAGE_TAG=v1.12.1
     - path: /etc/sysctl.d/max-user-watches.conf
       filesystem: root
       contents: