Revert of [recipe_modules/step] do not set cwd if it is start_dir.

recipe_modules/step/example.py

Index: recipe_modules/step/example.py
diff --git a/recipe_modules/step/example.py b/recipe_modules/step/example.py
index bd550c9f2f0fe6e5b1932cca6f94addb4ff877ba..3f7c69d81bf445f7612828a685644d229808dca7 100644
--- a/recipe_modules/step/example.py
+++ b/recipe_modules/step/example.py
@@ -18,12 +18,14 @@
 
 PROPERTIES = {
   'bad_return': recipe_api.Property(default=False),
+  'raise_infra_failure': recipe_api.Property(default=False),
   'access_invalid_data': recipe_api.Property(default=False),
   'timeout': recipe_api.Property(default=0, kind=int),
 }
 
 
-def RunSteps(api, bad_return, access_invalid_data, timeout):
+def RunSteps(
+    api, bad_return, raise_infra_failure, access_invalid_data, timeout):
   if bad_return:
     return RETURN_SCHEMA.new(test_me='this should fail')
   elif timeout:
@@ -42,17 +44,6 @@
   # The api.step object is directly callable.
   api.step('hello', ['echo', 'Hello World'])
   api.step('hello', ['echo', 'Why hello, there.'])
-
-  # You can change the current working directory as well
-  api.step('mk subdir', ['mkdir', 'something'])
-  with api.step.context({'cwd': api.path['start_dir'].join('something')}):
-    api.step('something', ['bash', '-c', 'echo Why hello, there, in a subdir.'])
-
-  # By default, all steps run in 'start_dir', or the cwd of the recipe engine
-  # when the recipe begins. Because of this, setting cwd to start_dir doesn't
-  # show anything in particular in the expectations.
-  with api.step.context({'cwd': api.path['start_dir']}):
-    api.step('start_dir ignored', ['bash', '-c', 'echo what happen'])
 
   # You can also manipulate various aspects of the step, such as env.
   # These are passed straight through to subprocess.Popen.
@@ -84,7 +75,7 @@
     api.step('goodbye', ['echo', 'goodbye'])
     # Modifying step_result now would raise an AssertionError.
   except api.step.StepFailure:
-    # Raising anything besides StepFailure or StepWarning causes the build to go
+    # Raising anything besides StepFailure or StepWarning causes the build to go 
     # purple.
     raise ValueError('goodbye must exit 0!')
 
@@ -166,6 +157,7 @@
 
   yield (
       api.test('infra_failure') +
+      api.properties(raise_infra_failure=True) +
       api.step_data('cleanup', retcode=1)
     )