WIP feat(helm): Add --node-selectors and --output flags to helm init

This feature enables users to specify more control over where Tiller pod
lands by allowing "node-selectors" to be specified. Alternatively, the
"--output" flag will skip install and dump Tiller's raw Deployment manifest
 to stdout so user may alter it as they see fit (probably with a JSON manipulation
  tool like jq).

Closes #2221

cmd/helm/installer/install.go

@@ -122,6 +122,7 @@ func generateLabels(labels map[string]string) map[string]string {
 func parseNodeSelectors(labels string) map[string]string {
 	kv := strings.Split(labels, ",")
 	nodeSelectors := map[string]string{}
+	nodeSelectors["beta.kubernetes.io/os"] = "linux"
 	for _, v := range kv {
 		el := strings.Split(v, "=")
 		if len(el) == 2 {