Use always_run v can_fail_build

scripts/slave/recipe_modules/step/api.py

Index: scripts/slave/recipe_modules/step/api.py
diff --git a/scripts/slave/recipe_modules/step/api.py b/scripts/slave/recipe_modules/step/api.py
index f23e7d6585947864054f0981a8d42f3af29e673e..b25aa916aaf07e29dc1a7d901a760d3bf2958409 100644
--- a/scripts/slave/recipe_modules/step/api.py
+++ b/scripts/slave/recipe_modules/step/api.py
@@ -36,6 +36,14 @@ class StepApi(recipe_api.RecipeApi):
     assert 'shell' not in kwargs
     assert isinstance(cmd, list)
 
+    if kwargs.get('abort_on_failure', False):
+      @recipe_api.wrap_followup(kwargs)
+      def assert_success(step_result):
+        if step_result.presentation.status == 'FAILURE':
+          raise recipe_api.RecipeAbort(
+            "Step(%s) failed and was marked as abort_on_failure" % name)
+      kwargs['followup_fn'] = assert_success
+
     cmd = list(cmd)  # Create a copy in order to not alter the input argument.
     if self.auto_resolve_conflicts:
       step_count = self._step_names.setdefault(name, 0) + 1