Refactor producer invocation in cucumber features:

Use "When I successfully execute" instead of "When I execute", and
assert that exit status code was successful in this new step.

features/tasks/condition.feature

@@ -9,6 +9,5 @@ Feature: `condition' task keyword
         echo 'evaluated'
       end
       """
-    When I execute the recipe
-    Then the exit status must be 0
+    When I successfully execute the recipe
     And the output must not contain "evaluated"