code: func (s *Sentinel) putToBottom(addr string) {
  	addrs := s.Addrs
  	if addrs[len(addrs)-1] == addr {
  		// Already on bottom.
  		return
  	}
  	newAddrs := []string{}
  	for _, a := range addrs {
  		if a == addr {
  			continue
  		}
  		newAddrs = append(newAddrs, a)
  	}
  	newAddrs = append(newAddrs, addr)
  	s.Addrs = newAddrs
  }
docs: // putToBottom puts Sentinel address to the bottom of address list.
  // We call this method internally when see that some Sentinel failed to answer
  // on application request so next time we start with another one.
  //
  // Lock must be held by caller.