Missing keeper in update variants for `enable_gcfs` node pool option

[lauraseidler]

TL;DR

Adding the gcfs_config block (controlled through enable_gcfs option for node pools) forces the node pool to get re-created, but the keeper is missing for the update variants, causing the apply to fail.

Expected behavior

New node pool gets created, and then the old node pool gets destroyed.

Observed behavior

Upgrade fails, as node pool with the same name already exists.

Terraform Configuration

Any update-variant cluster with a node pool that was created before #1174 got merged

Terraform Version

$ terraform version      
Terraform v1.1.8
on linux_amd64
+ provider registry.terraform.io/hashicorp/external v2.2.2
+ provider registry.terraform.io/hashicorp/google v4.10.0
+ provider registry.terraform.io/hashicorp/google-beta v4.10.0
+ provider registry.terraform.io/hashicorp/kubernetes v2.9.0
+ provider registry.terraform.io/hashicorp/null v3.1.1
+ provider registry.terraform.io/hashicorp/random v3.1.2
+ provider registry.terraform.io/hashicorp/time v0.7.2

Additional information

I'll provide a PR for this shortly.

Note: Enabling/disabling image streaming via gcloud is possible without re-creating the node pool, but this doesn't seem to be supported by the current provider version.