Checks whether a V1 or V2 checkpoint exists with the specified prefix.
This is the recommended way to check if a checkpoint exists, since it takes into account the naming difference between V1 and V2 formats.
checkpoint_prefix: the prefix of a V1 or V2 checkpoint, with V2 taking priority. Typically the result of
Saver.save()or that of
tf.train.latest_checkpoint(), regardless of sharded/non-sharded or V1/V2.
A bool, true iff a checkpoint referred to by