Fix IP-alias subnet creation logic

cluster/gce/util.sh

@@ -1731,12 +1731,6 @@ function create-subnetworks() {
     --region ${REGION} \
     ${IP_ALIAS_SUBNETWORK} 2>/dev/null)
   if [[ -z ${subnet} ]]; then
-    # Only allow auto-creation for default subnets
-    if [[ ${IP_ALIAS_SUBNETWORK} != ${INSTANCE_PREFIX}-subnet-default ]]; then
-      echo "${color_red}Subnetwork ${NETWORK}:${IP_ALIAS_SUBNETWORK} does not exist${color_norm}"
-      exit 1
-    fi
-
     echo "Creating subnet ${NETWORK}:${IP_ALIAS_SUBNETWORK}"
     gcloud beta compute networks subnets create \
       ${IP_ALIAS_SUBNETWORK} \