Warn during warning.

slapos/recipe/build.py

@@ -107,7 +107,7 @@ class Script:
   def _checkPromise(self, promise_key, location):
     promise_text = self.options.get(promise_key)
     if promise_text is None:
-      self.logger.warning('Promise %r not defined' % promise_key)
+      self.logger.warning('Warning, promise %r not defined' % promise_key)
       return True
     promise_problem_list = []
     a = promise_problem_list.append