Fix node pool tests.

[nat-henderson]

The core problem here is that the available node versions are such that
version (max - 1) is not compatible with the latest master version.

Fixes hashicorp/terraform-provider-google#6283.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 40 deletions(-))
Terraform Beta: Diff ( 1 file changed, 40 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 88 deletions(-))
Terraform Beta: Diff ( 1 file changed, 88 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 4 insertions(+), 1 deletion(-))
Terraform Beta: Diff ( 1 file changed, 4 insertions(+), 1 deletion(-))

[danawillow]

Anything preventing this from getting in?

[nat-henderson]

Just the review! I'll assign you?