[sk] Add logging during asset upload, tweak creation subprocess
[sk] Add logging during asset upload, tweak creation subprocess

Change-Id: If432e9737362f71bc95e1f717b5a8d81e69c0f95
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/423018
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot