goldctl - Fallback to the python version of gsutil on windows.
goldctl - Fallback to the python version of gsutil on windows.

Change-Id: I55f53d10fc403b45a63871854e0b0e6c77e753fa
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/222463
Reviewed-by: Ben Wagner aka dogben <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@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