Add ability to dockerize kubelet in local cluster

cluster/images/kubelet/Dockerfile

@@ -1,8 +1,7 @@
 FROM centos
 ADD kubelet /kubelet
 RUN chmod a+rx /kubelet
-ADD nsenter /nsenter
-RUN chmod a+rx /nsenter
+RUN cp /usr/bin/nsenter /nsenter
 
 VOLUME /var/lib/docker
 VOLUME /var/lib/kubelet

cluster/images/kubelet/Makefile

@@ -2,15 +2,19 @@
 
 # TODO: figure out the best base image
 # TODO: figure out how to best source the nsenter binary, if necessary
-
+# TODO: figure out how to make a single source of version info for these
+#       images
 VERSION=v0.16
 
-release:
+release: clean
 	curl -O https://storage.googleapis.com/kubernetes-release/release/${VERSION}/bin/linux/amd64/kubelet
 	docker build -t gcr.io/google_containers/kubelet:${VERSION} .
 	gcloud preview docker push gcr.io/google_containers/kubelet:${VERSION}
 
 local:
-	docker build -t gcr.io/google_containers/kubelet:${VERSION} .
+	docker build -t gcr.io/google_containers/kubelet .
+
+clean:
+	rm -f kubelet
 
 .PHONY: release