Fix issues in assets scripts

- Delete unconditionally uses 'gsutil'
- args.gsutil not plumbed properly

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2326663002

Review-Url: https://codereview.chromium.org/2326663002
diff --git a/infra/bots/assets/asset_utils.py b/infra/bots/assets/asset_utils.py
index 8a1404f..ae58d45 100644
--- a/infra/bots/assets/asset_utils.py
+++ b/infra/bots/assets/asset_utils.py
@@ -198,11 +198,11 @@
     gs_path = GS_SUBDIR_TMPL % (self._gs_bucket, name)
     attempt_delete = True
     try:
-      subprocess.check_call(['gsutil', 'ls', gs_path])
+      subprocess.check_call(self._gsutil + ['ls', gs_path])
     except subprocess.CalledProcessError:
       attempt_delete = False
     if attempt_delete:
-      subprocess.check_call(['gsutil', 'rm', '-rf', gs_path])
+      subprocess.check_call(self._gsutil + ['rm', '-rf', gs_path])
 
 
 class MultiStore(object):
diff --git a/infra/bots/assets/assets.py b/infra/bots/assets/assets.py
index b398988..3265a63 100755
--- a/infra/bots/assets/assets.py
+++ b/infra/bots/assets/assets.py
@@ -25,23 +25,27 @@
 
 def add(args):
   """Add a new asset."""
-  asset_utils.Asset.add(args.asset_name, asset_utils.MultiStore())
+  asset_utils.Asset.add(args.asset_name,
+                        asset_utils.MultiStore(gsutil=args.gsutil))
 
 
 def remove(args):
   """Remove an asset."""
-  asset_utils.Asset(args.asset_name, asset_utils.MultiStore()).remove()
+  asset_utils.Asset(args.asset_name,
+                    asset_utils.MultiStore(gsutil=args.gsutil)).remove()
 
 
 def download(args):
   """Download the current version of an asset."""
-  asset = asset_utils.Asset(args.asset_name, asset_utils.MultiStore())
+  asset = asset_utils.Asset(args.asset_name,
+                            asset_utils.MultiStore(gsutil=args.gsutil))
   asset.download_current_version(args.target_dir)
 
 
 def upload(args):
   """Upload a new version of the asset."""
-  asset = asset_utils.Asset(args.asset_name, asset_utils.MultiStore())
+  asset = asset_utils.Asset(args.asset_name,
+                            asset_utils.MultiStore(gsutil=args.gsutil))
   asset.upload_new_version(args.target_dir, commit=args.commit)