Enable strict coverage for step module

recipe_modules/step/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')