[infra] Move GCE tasks to smaller/larger VMs. Bug: skia:7415, skia:7416 Change-Id: Ibdd391dce62ff16bfc7fa8d860c3cbcaddab7c4d Reviewed-on: https://skia-review.googlesource.com/124340 Reviewed-by: Eric Boren <borenet@google.com> Commit-Queue: Ben Wagner <benjaminwagner@google.com>