message: Fix get_ident import in python2
  Reviewers: #tensorflow, georgep
  Subscribers: georgep
diff: @@ -23,6 +23,7 @@ from __future__ import print_function
  import collections
  import threading
  +from six.moves import _thread
  import six
  from tensorflow.compiler.plugin.poplar.driver.config_pb2 import IpuOptions
  @@ -178,7 +179,7 @@ class _FeedIdAllocator:
  # The infeeds are deleted after each IPUEstimator function call,
  # so the ID only needs to be different for function calls that can
  # overlap (e.g. from different threads).
  - thread_id = threading.get_ident()
  + thread_id = _thread.get_ident()
  with cls._lock:
  if not thread_id in cls._infeed_thread_ids:
  