Switch machine-type for Coverage tasks.

Coverage doesn't seem to deal well with multiple threads. Using 2-core
VMs is faster than using 64-core VMs.

On the other hand, the Coverage Upload task performs much better on a
64-core VM.

Bug: skia:7415
No-Try: true
Change-Id: Ieb58fc47970dd66fa64cf6a8c9de1f9236e2f3a0
Reviewed-on: https://skia-review.googlesource.com/127053
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
2 files changed