Add vpython support to Python recipe module.

recipe_modules/python/example.py

 # Copyright 2015 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.
 
 """Launches the repo bundler."""
 
 DEPS = [
+  'path',
   'python',
   'raw_io',
   'step',
 ]
 
 
 def RunSteps(api):
   api.python.succeeding_step("success", ["This step is a success"],
                              as_log='success')
 
   # Test that a failing step raises StepFailure.
   was_failure = False
   try:
     api.python.failing_step("failure", "This step is a failure :(")
   except api.step.StepFailure:
     was_failure = True
   assert was_failure
 
   # Test that unbufferred actually removes PYTHONUNBUFFERED envvar.
   api.python('run json.tool', '-m', [
     'json.tool', api.raw_io.input('{"something":[true,true]}'),
   ], unbuffered=False)
 
   api.python.inline('inline', 'print "Hello World!"')
 
+  # Test "vpython"-based invocation.
+  api.python('run vpython.script', api.resource('test.py'), venv=True)

[iannucci, 2017/05/10 22:46:14]

let's do test_embedded.py and test_external.py 

+  api.python('run vpython.spec', api.resource('test.py'), args=['--verify'],
+             venv=api.resource('test.vpython'))
+
 
 def GenTests(api):
   yield api.test('basic')