Don't fail teardown if we can't delete the network

cluster/gce/util.sh

@@ -1362,7 +1362,7 @@ function kube-down() {
     "${NETWORK}-default-ssh" \
     "${NETWORK}-default-internal"  # Pre-1.5 clusters
   if [[ "${KUBE_DELETE_NETWORK}" == "true" ]]; then
-    delete-network
+    delete-network || true  # might fail if there are leaked firewall rules
   fi
 
   # If there are no more remaining master replicas, we should update kubeconfig.

cluster/gke/util.sh

@@ -387,7 +387,6 @@ function test-teardown() {
       if ! "${GCLOUD}" compute networks delete --project "${PROJECT}" --quiet "${NETWORK}"; then
         echo "Failed to delete network '${NETWORK}'. Listing firewall-rules:"
         "${GCLOUD}" compute firewall-rules --project "${PROJECT}" list --filter="network=${NETWORK}"
-        return 1
       fi
     fi
   fi