Automatic merge from submit-queue (batch tested with PRs 51108, 51035, 50539, 51160, 50947)

Auto-calculate CLUSTER_IP_RANGE based on cluster size

In preparation for eliminating CLUSTER_IP_RANGE env var from job configs, making it less error prone while folks try to start their own large cluster tests (https://github.com/kubernetes/kubernetes/issues/50907).

/cc @kubernetes/sig-scalability-misc @wojtek-t @gmarek