Return a list of IPs of the nameservers for ``domain``

    If ``resolve`` is False, don't resolve names.

    CLI Example:

    .. code-block:: bash

        salt ns1 dig.NS google.com

def NS(domain, resolve=True, nameserver=None):
    '''
    Return a list of IPs of the nameservers for ``domain``

    If ``resolve`` is False, don't resolve names.

    CLI Example:

    .. code-block:: bash

        salt ns1 dig.NS google.com
    '''
    dig = ['dig', '+short', six.text_type(domain), 'NS']

    if nameserver is not None:
        dig.append('@{0}'.format(nameserver))

    cmd = __salt__['cmd.run_all'](dig, python_shell=False)
    # In this case, 0 is not the same as False
    if cmd['retcode'] != 0:
        log.warning(
            'dig returned exit code \'%s\'. Returning empty list as fallback.',
            cmd['retcode']
        )
        return []

    if resolve:
        ret = []
        for ns_host in cmd['stdout'].split('\n'):
            for ip_addr in A(ns_host, nameserver):
                ret.append(ip_addr)
        return ret

    return cmd['stdout'].split('\n')