cos-customizer: install-gpu: Auth with GCS

Currently, cos-customizer lists gs://nvidia-drivers-us-public as an
anonymous user. It probably does this to simplify running cos-customizer
outside of cloud build.

Nvidia recently changed their bucket permissions to disallow anonymous
users from accessing it. So cos-customizer fails when it tries to read
gs://nvidia-drivers-us-public as an anonymous user.

Since the use case outside of cloud build isn't super important, let's
stop listing that bucket as an anonymous user to get things working
again.

BUG=b/217461037
TEST=`gcloud builds submit --config=testing/gpu_test.yaml`

Change-Id: If3e0ed6f33fe0f30165e4ff49bf7b446b581d7d2
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/28842
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: He Gao <hegao@google.com>
diff --git a/src/cmd/cos_customizer/install_gpu.go b/src/cmd/cos_customizer/install_gpu.go
index 2a7876c..dd45b8c 100644
--- a/src/cmd/cos_customizer/install_gpu.go
+++ b/src/cmd/cos_customizer/install_gpu.go
@@ -263,7 +263,7 @@
 	if !ok {
 		log.Panic("InstallGPU expects two arguments; *fs.Files and ServiceClients")
 	}
-	_, gcsClient, err := serviceClients(ctx, true)
+	_, gcsClient, err := serviceClients(ctx, false)
 	if err != nil {
 		log.Println(err)
 		return subcommands.ExitFailure