env/windows: add network option to build.bash

Tweak target instance creation in build.bash to select proper network.

Updates golang/go#35006.

Change-Id: Icd0cc4dc75fdf2ee7d0b5b7c77e4fd3c33135bc3
Reviewed-on: https://go-review.googlesource.com/c/build/+/406854
Reviewed-by: Alex Rakoczy <alex@golang.org>
diff --git a/env/windows/build.bash b/env/windows/build.bash
index d40afdb..c0aed31 100755
--- a/env/windows/build.bash
+++ b/env/windows/build.bash
@@ -70,6 +70,7 @@
 gcloud compute instances create --machine-type="$MACHINE_TYPE" "$INSTANCE_NAME" \
         --image "$BASE_IMAGE" --image-project "$IMAGE_PROJECT" \
         --project="$PROJECT_ID" --zone="$ZONE" \
+        --network=default-vcp \
         --metadata="buildlet-binary-url=https://storage.googleapis.com/go-builder-data/buildlet.windows-amd64" \
         --metadata-from-file=windows-startup-script-ps1=startup.ps1