Add --create-subnetwork field as setting ipv6 access type is supported only with this option

Author: shaun-nx

tests/scripts/create-gke-cluster.sh

@@ -34,6 +34,7 @@ gcloud container clusters create "${GKE_CLUSTER_NAME}" \
     --no-enable-insecure-kubelet-readonly-port \
     --stack-type="${GKE_CLUSTER_STACK_TYPE}" \
     --ipv6-access-type="${GKE_CLUSTER_IPV6_ACCESS_TYPE}" \
+    --create-subnetwork name=${RESOURCE_NAME},range=/21 
 
 # Add current IP to GKE master control node access, if this script is not invoked during a CI run.
 if [ "${IS_CI}" = "false" ]; then