Converts checkpoint data to GraphDef.
tf.contrib.model_pruning.graph_def_from_checkpoint( checkpoint_dir, output_node_names )
Reads the latest checkpoint data and produces a GraphDef in which the variables have been converted to constants.
checkpoint_dir: Path to the checkpoints.
output_node_names: List of name strings for the result nodes of the graph.
A GraphDef from the latest checkpoint
ValueError: if no checkpoint is found