Return abspath to file with item content.

    Fetches the file from remote storage if required.

def overlay(overlay_name, dataset_uri, item_identifier):
    """Return abspath to file with item content.

    Fetches the file from remote storage if required.
    """
    dataset = dtoolcore.DataSet.from_uri(dataset_uri)
    if overlay_name not in dataset.list_overlay_names():
        click.secho(
            "No such overlay in dataset: {}".format(overlay_name),
            fg="red",
            err=True
        )
        sys.exit(4)
    overlay = dataset.get_overlay(overlay_name)

    try:
        click.secho(str(overlay[item_identifier]))
    except KeyError:
        click.secho(
            "No such identifier in overlay: {}".format(item_identifier),
            fg="red",
            err=True
        )
        sys.exit(5)