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/recipes/target.feature

@@ -7,6 +7,5 @@ Feature: `target' recipe keyword
 
       puts env.target
       """
-    When I execute the recipe
-    Then the exit status must be 0
+    When I successfully execute the recipe
     And the output must contain exactly "some_host.example\n"