kubernetes: fix, test GetNodes

Broken in my cleanup golang.org/cl/36692

Change-Id: I5f82314b8ff703cf2c894771fbc0eb16834fc47b
Reviewed-on: https://go-review.googlesource.com/37216
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/kubernetes/client.go b/kubernetes/client.go
index a99a5fd..9e42b89 100644
--- a/kubernetes/client.go
+++ b/kubernetes/client.go
@@ -429,7 +429,7 @@
 // PodNodes returns the list of nodes that comprise the Kubernetes cluster
 func (c *Client) GetNodes(ctx context.Context) ([]api.Node, error) {
 	var list api.NodeList
-	if err := c.do(ctx, "GET", c.nsEndpoint()+"nodes", &list); err != nil {
+	if err := c.do(ctx, "GET", c.endpointURL+"/nodes", &list); err != nil {
 		return nil, err
 	}
 	return list.Items, nil