Use right bucket for buildstats

Additionally, include the revision name in the json file name
to avoid collisions.

Bug: skia:
Change-Id: I6601c28679f82406721d740041a60077b460c0f4
Reviewed-on: https://skia-review.googlesource.com/c/160560
Reviewed-by: Eric Boren <borenet@google.com>
5 files changed