Automatic merge from submit-queue Add parallelism to GCE cluster upgrade Fixes https://github.com/kubernetes/kubernetes/issues/48373 Should allow upgrading 500-node cluster (1.6->1.7) in < 1 hr. It currently takes ~1.5 day. Though it is the duty of the upgrader to choose the right parallelism in order to avoid disrupting too many pods. /cc @kubernetes/sig-cluster-lifecycle-pr-reviews @kubernetes/sig-scalability-misc @mikedanese @gmarek