message: Limit the amount of logspam a use of GraphKeys.VARIABLES causes.
  Multiple copies of this warning next to each other often make logs unreadable.
diff: @@ -4938,9 +4938,10 @@ class GraphKeys(object):
  @decorator_utils.classproperty
  def VARIABLES(cls): # pylint: disable=no-self-argument
  - logging.warning("VARIABLES collection name is deprecated, "
  - "please use GLOBAL_VARIABLES instead; "
  - "VARIABLES will be removed after 2017-03-02.")
  + logging.log_first_n(logging.WARN,
  + "VARIABLES collection name is deprecated, please use "
  + "GLOBAL_VARIABLES instead; VARIABLES will be removed "
  + "after 2017-03-02.", 1)
  return cls.GLOBAL_VARIABLES
  