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/actions/echo.feature

@@ -7,6 +7,5 @@ Feature: `echo' task action
         echo 'hello'
       end
       """
-    When I execute the recipe
-    Then the exit status must be 0
+    When I successfully execute the recipe
     And the output must contain exactly "hello\n"

features/actions/sh.feature

@@ -22,7 +22,7 @@ Feature: sh task action
         sh '\echo from remote'
       end
       """
-    When I execute the recipe
+    When I successfully execute the recipe
     Then the output must contain "from remote"
 
   Scenario: aborts on failed command execution