Rename client Minions->Nodes, select the correct path for v1beta3

Replaces the client public interface but leaves old references to "minions"
for a later refactor.  Selects the path "nodes" for v1beta3 and "minions"
for older versions.

pkg/master/master.go

@@ -316,7 +316,7 @@ func (m *Master) init(c *Config) {
 			PodCache:      podCache,
 			PodInfoGetter: c.KubeletClient,
 			Registry:      m.podRegistry,
-			Minions:       m.client.Minions(),
+			Nodes:         m.client.Nodes(),
 		}),
 		"replicationControllers": controller.NewREST(m.controllerRegistry, m.podRegistry),
 		"services":               service.NewREST(m.serviceRegistry, c.Cloud, m.minionRegistry, m.portalNet),