Generic service type handler for kompose

Moved label handling code from Transformer to loader,
to make it generic to handle creating service types.

Added new attribute to ServiceConfig which gets populated
in loader.

Fixes #273

pkg/loader/compose/compose.go

@@ -207,6 +207,16 @@ func (c *Compose) LoadFile(file string) kobject.KomposeObject {
 				}
 			}
 
+			// canonical "Custom Labels" handler
+			// Labels used to influence conversion of kompose will be handled
+			// from here for docker-compose. Each loader will have such handler.
+			for key, value := range composeServiceConfig.Labels {
+				switch key {
+				case "kompose.service.type":
+					serviceConfig.ServiceType = handleServiceType(value)
+				}
+			}
+
 			// convert compose labels to annotations
 			serviceConfig.Annotations = map[string]string(composeServiceConfig.Labels)
 
@@ -227,3 +237,17 @@ func (c *Compose) LoadFile(file string) kobject.KomposeObject {
 
 	return komposeObject
 }
+
+func handleServiceType(ServiceType string) string {
+	switch strings.ToLower(ServiceType) {
+	case "", "clusterip":
+		return string(api.ServiceTypeClusterIP)
+	case "nodeport":
+		return string(api.ServiceTypeNodePort)
+	case "loadbalancer":
+		return string(api.ServiceTypeLoadBalancer)
+	default:
+		logrus.Fatalf("Unknown value '%s', supported values are 'NodePort, ClusterIP or LoadBalancer'", ServiceType)
+		return ""
+	}
+}