[build-images] --remote_download_toplevel to avoid unnecessary downloads

Change-Id: I916e703298f4290f30853cdf1b2d0751bbc782f3
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/600317
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Eric Boren <borenet@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
diff --git a/cd/go/build-images/build.go b/cd/go/build-images/build.go
index e72d6d9..bf21fa0 100644
--- a/cd/go/build-images/build.go
+++ b/cd/go/build-images/build.go
@@ -81,7 +81,7 @@
 
 	cmd := []string{"bazelisk", "run"}
 	if rbe {
-		cmd = append(cmd, "--config=remote", "--google_default_credentials")
+		cmd = append(cmd, "--config=remote", "--google_default_credentials", "--remote_download_toplevel")
 	}
 	cmd = append(cmd, target)
 	if _, err := exec.RunCwd(ctx, cwd, cmd...); err != nil {