Rename a key, when an instance has also been renamed

def rename_key(pki_dir, id_, new_id):
    '''
    Rename a key, when an instance has also been renamed
    '''
    oldkey = os.path.join(pki_dir, 'minions', id_)
    newkey = os.path.join(pki_dir, 'minions', new_id)
    if os.path.isfile(oldkey):
        os.rename(oldkey, newkey)