Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Remake cluster size autoscaling scale to zero test
This PR affects only cluster size autoscaling test suite. Changes:
* check whether autoscaling for is enabled by looking for a node group with a given max number of nodes instead of min as the field is omitted if value is 0
* split scale to zero test into GKE & GCE versions, add GKE-specific setup and verification
83d3137e25