code: def server_link(rel, server_id=None, self_rel=False):
      
      servers_href = '/v1/servers'
      link = _SERVER_LINKS[rel].copy()
      link['href'] = link['href'].format(**locals())
      link['rel'] = 'self' if self_rel else rel
      return link
docs: Helper for getting a Server link document, given a rel.