CI: GKE-based: network "default" does not have available private IP space in 10.0.0.0/8 to reserve a /14 block

[tklauser]

GKE-based workflows (GKE, external workloads, multicluster) occasionally fail during cluster creation with the following error:

The network "default" does not have available private IP space in 10.0.0.0/9 to reserve a /14 block for pods for cluster 

Examples:

• Scheduled run on master: https://github.com/cilium/cilium-cli/runs/7000764590?check_suite_focus=true
• PR #933: https://github.com/cilium/cilium-cli/runs/6993592366?check_suite_focus=true

I assume this can happen if too many clusters are created simultaneously. One option to work around this would be to specify --cluster-ipv4-cider on gcloud container clusters create. Also see https://stackoverflow.com/questions/42129327/gke-cluster-creation-fails-because-the-network-default-does-not-have-available