Automatic merge from submit-queue

In cluster scripts correct gcloud list arg from '--zone' to '--zones'

I started getting these messages when doing `kube-up` and similar operations:

    WARNING: Abbreviated flag [--zone] will be disabled in release 132.0.0, use the full name [--zones].

This PR corrects the flag where used.

Note there are many uses of `--zone` on commands like `gcloud instances describe` which are still correct - those commands do not accept multiple zones.