Upgrade to coverage 3.7.1 and have it auto-build itself on first use.

scripts/slave/unittests/recipe_simulation_test.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Provides simulator test coverage for individual recipes."""
 
 import os
 
 # Importing for side effects on sys.path? Yes... yes we are :(
-import test_env  # pylint: disable=W0611
+import test_env  # pylint: disable=W0611,W0403
 
 from common import annotator
 from slave import annotated_run
 from slave import recipe_config_types
 from slave import recipe_loader
 from slave import recipe_util
 
-import expect_tests
+import expect_tests  # pylint: disable=W0403
 
 
 def RunRecipe(test_data):
   stream = annotator.StructuredAnnotationStream(stream=open(os.devnull, 'w'))
   recipe_config_types.ResetTostringFns()
   # TODO(iannucci): Only pass test_data once.
   result = annotated_run.run_steps(stream, test_data.properties,
                                    test_data.properties, test_data)
   return expect_tests.Result([s.step for s in result.steps_ran.itervalues()])
 
@@ skipping 19 matching lines @@
       )
 
 
 if __name__ == '__main__':
   expect_tests.main('recipe_simulation_test', GenerateTests, (
       [os.path.join(x, '*') for x in recipe_util.RECIPE_DIRS()] +
       [os.path.join(x, '*', '*api.py') for x in recipe_util.MODULE_DIRS()]
   ), (
       [os.path.join(x, '*', '*config.py') for x in recipe_util.MODULE_DIRS()]
   ))