Fixing execution state_info

* Now engine checks for all failed tasks
   and then assign state_info using messages
   from their action executions

Closes-Bug: #1476075

Change-Id: I7f6e0d0e59cf89c0204047515e6d62cc3adce304

mistral/workflow/base.py

@@ -62,6 +62,15 @@ class WorkflowController(object):
 
         return self._find_next_commands()
 
+    @abc.abstractmethod
+    def is_error_handled_for(self, task_ex):
+        """Determines if error is handled for specific task.
+
+        :return: True if either there is no error at all or
+            error is considered handled.
+        """
+        raise NotImplementedError
+
     @abc.abstractmethod
     def all_errors_handled(self):
         """Determines if all errors (if any) are handled.