gsutil: use lib.gs API for commands

We want to get away from exposing the direct path to the gsutil program,
so convert this wrapper script to use our wrapper command API.

BUG=b:188645230
TEST=`./scripts/gsutil ls gs://chromiumos-sdk/` works

Change-Id: Ica514c9f57878552cc9d8623063897bb2df6ba2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2980313
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Commit-Queue: Sergey Frolov <sfrolov@google.com>
diff --git a/scripts/gsutil.py b/scripts/gsutil.py
index 08caffc..da1b375 100644
--- a/scripts/gsutil.py
+++ b/scripts/gsutil.py
@@ -7,11 +7,10 @@
 This takes care of downloading the pinned version we use in chromite.
 """
 
-import os
-
 from chromite.lib import gs
 
 
 def main(argv):
-  gsutil = gs.GSContext.GetDefaultGSUtilBin()
-  os.execv(gsutil, ['gsutil'] + argv)
+  ctx = gs.GSContext(retries=0)
+  return ctx.DoCommand(
+      argv, print_cmd=False, stderr=None, check=False).returncode