List the installed versions of python.

    CLI Example:

    .. code-block:: bash

        salt '*' pyenv.versions

def versions(runas=None):
    '''
    List the installed versions of python.

    CLI Example:

    .. code-block:: bash

        salt '*' pyenv.versions
    '''
    ret = _pyenv_exec('versions', '--bare', runas=runas)
    return [] if ret is False else ret.splitlines()