Return server version from varnishd -V

    CLI Example:

    .. code-block:: bash

        salt '*' varnish.version

def version():
    '''
    Return server version from varnishd -V

    CLI Example:

    .. code-block:: bash

        salt '*' varnish.version
    '''
    cmd = ['varnishd', '-V']
    out = __salt__['cmd.run'](cmd, python_shell=False)
    ret = re.search(r'\(varnish-([^\)]+)\)', out).group(1)
    return ret