dev: Let devserver use gsutil functions in chromite.

Together with CL:378576, this CL is to make platform/dev to use GS-related
functions in chromite. This could help reduce the maintain cost and
inconsistency errors caused by different versions of gsutil.

BUG=chromium:640609
TEST=Ran unittest.
Test 2 functions with local devserver: trigger_download &
get_latest_build_in_gs (including xbuddy/latest, xbuddy/latest-official,
xbuddy/latest-{dev|beta|stable}, xbuddy/latest-R53).

Change-Id: I27f97ebebb76ea6b6b5ef9cc4d5b81c524f6968c
Reviewed-on: https://chromium-review.googlesource.com/381693
Commit-Ready: Xixuan Wu <xixuan@chromium.org>
Tested-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
3 files changed