Add dockerless tags to all files in dockershim

As the final step, add the `dockerless` tags to all files in the
dockershim. Using `-tags=dockerless` in `go build`, we can compile
kubelet without the dockershim.

Once cadvisor no longer depends on `docker/docker`, compiling with
`-tags=dockerless` should be sufficient to compile the Kubelet w/o a
dependency on `docker/docker`.

pkg/kubelet/dockershim/network/testing/plugins_test.go

@@ -1,3 +1,5 @@
+// +build !dockerless
+
 /*
 Copyright 2014 The Kubernetes Authors.