How to use the stacker.hooks.utils.full_path function in stacker

def read_public_key_file(path):
    try:
        with open(utils.full_path(path), 'rb') as f:
            data = f.read()

        if not data.startswith(b"ssh-rsa"):
            raise ValueError(
                "Bad public key data, must be an RSA key in SSH authorized "
                "keys format (beginning with `ssh-rsa`)")

        return data.strip()
    except (ValueError, IOError, OSError) as e:
        logger.error("Failed to read public key file {}: {}".format(
            path, e))
        return None

paths[key] = path

    parameters = {
        "ServerCertificateName": kwargs.get("cert_name"),
    }

    for key, path in paths.items():
        if not path:
            continue

        # Allow passing of file like object for tests
        try:
            contents = path.read()
        except AttributeError:
            with open(utils.full_path(path)) as read_file:
                contents = read_file.read()

        if key == "certificate":
            parameters["CertificateBody"] = contents
        elif key == "private_key":
            parameters["PrivateKey"] = contents
        elif key == "chain":
            parameters["CertificateChain"] = contents

    return parameters

def create_key_pair_local(ec2, keypair_name, dest_dir):
    dest_dir = utils.full_path(dest_dir)
    if not os.path.isdir(dest_dir):
        logger.error("\"%s\" is not a valid directory", dest_dir)
        return None

    file_name = "{0}.pem".format(keypair_name)
    key_path = os.path.join(dest_dir, file_name)
    if os.path.isfile(key_path):
        # This mimics the old boto2 keypair.save error
        logger.error("\"%s\" already exists in \"%s\" directory",
                     file_name, dest_dir)
        return None

    # Open the file before creating the key pair to catch errors early
    with open(key_path, "wb") as f:
        keypair = create_key_pair(ec2, keypair_name)
        f.write(keypair["KeyMaterial"].encode("ascii"))