message: Ensure the server_def is stored in Context
  The current code only stored the server_def when the context had not yet
  been initialized.
diff: @@ -392,9 +392,10 @@ class Context(object):
  """
  if not server_def:
  raise ValueError("server_def is None.")
  - if not self._context_handle:
  +
  self._server_def = server_def
  - else:
  +
  + if self._context_handle:
  server_def_str = server_def.SerializeToString()
  pywrap_tensorflow.TFE_ContextSetServerDef(self._context_handle,
  keep_alive_secs, server_def_str)
  