dashboard: Update name of Docker image for Kubernetes builder.

The Makefile used to create the Docker image used by the Kubernetes builder
creates an image with a different name than the dashboard expects. This
change updates the dashboard to pull the image created by the Makefile.

Change-Id: Idcf8f5867d9995205c6c8482a7e8bfa1b63d9551
Reviewed-on: https://go-review.googlesource.com/28416
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 7d9bb7b..07bfbac 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -24,7 +24,7 @@
 var Hosts = map[string]*HostConfig{
 	"host-linux-kubestd": &HostConfig{
 		Notes:           "Kubernetes container on GKE.",
-		KubeImage:       "linux-x86-std:latest",
+		KubeImage:       "linux-x86-std-kube:latest",
 		buildletURLTmpl: "http://storage.googleapis.com/$BUCKET/buildlet.linux-amd64",
 		env:             []string{"GOROOT_BOOTSTRAP=/go1.4"},
 	},