devserver:  Fix Download call.

The download call no longer takes an async parameter, fix the
call.

Move to python3, Moblab has been using python3 for devserver for some
time.

TEST=stage build on local moblab
BUG=chromium:1143147

Change-Id: If72b637b61ae3d1a6c07722f42dd92f4940ed016
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2505499
Tested-by: Keith Haddow <haddowk@chromium.org>
Auto-Submit: Keith Haddow <haddowk@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
1 file changed