Returns public and private key paths for a given key_name.

def key_pair_paths(key_name):
    """Returns public and private key paths for a given key_name."""
    public_key_path = os.path.expanduser("~/.ssh/{}.pub".format(key_name))
    private_key_path = os.path.expanduser("~/.ssh/{}.pem".format(key_name))
    return public_key_path, private_key_path