Update Presubmit to python3

Recipe-Nontrivial-Roll: build
Bug:1370463
Change-Id: I0bf182badc16f0d75c7330f52906f4cf9ff66e08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3975294
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Riley Wong <rgw@google.com>

recipes/recipe_modules/presubmit/api.py

@@ -30,7 +30,7 @@ class PresubmitApi(recipe_api.RecipeApi):
 
     name = kwargs.pop('name', 'presubmit')
     with self.m.depot_tools.on_path():
-      cmd = ['vpython', self.presubmit_support_path]
+      cmd = ['vpython3', self.presubmit_support_path]
       cmd.extend(args)
       cmd.extend(['--json_output', self.m.json.output()])
       if self.m.resultdb.enabled:

recipes/recipe_modules/presubmit/examples/full.expected/basic.json

@@ -1,7 +1,7 @@
 [
   {
     "cmd": [
-      "vpython",
+      "vpython3",
       "RECIPE_REPO[depot_tools]/presubmit_support.py",
       "--json_output",
       "/path/to/tmp/json"