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Fix disruptive regional tests 3

With GKE multizonal and regional clusters (when nodes are in created in more than one zones), in test framework we are passing:
1. --num-nodes equal to number of nodes in a single zone
2. --node-instance-groups equal to MIG names in that zone
The (1) is consistent with end-user experience, since the same semantic for "--num-nodes" is used in gcloud. (2) is strictly connected to that, and we don't want to change that.

As a result, the number of expected nodes, mig size etc. can't be explicitly based on those numbers. Also commands for nodes restarts etc. need to be splitted across zones and correct zone parameter has to be passed.