Enable strict coverage for step module

recipes/engine_tests/trigger.py

-# Copyright 2013 The LUCI Authors. All rights reserved.
-# Use of this source code is governed under the Apache License, Version 2.0
-# that can be found in the LICENSE file.
-
-from recipe_engine.recipe_api import Property
-
-DEPS = [
-    'properties',
-    'step',
-]
-
-PROPERTIES = {
-    'command': Property(default=None),
-}
-
-def RunSteps(api, command):
-  api.step(
-      'trigger some junk',
-      cmd=command,
-      trigger_specs=[{
-          'builder_name': 'triggered',
-          'buildbot_changes': [{
-              'when_timestamp': 1445412480,
-          }],
-      }])
-
-def GenTests(api):
-  yield api.test('basic')