Yicheng Qin 331ecdf8c8 client: return correct error for 50x response
etcd always returns 500/503 response when it may have no leader.
So we should log the other 50x response in a normal way.

This helps to log correctly when discovery meets 504 error. Before this
PR, it logs like this:

```
18:31:58 etcd2 | 2015/08/4 18:31:58 discovery: error #0: client: etcd
member https://discovery.etcd.io has no leader
18:31:58 etcd2 | 2015/08/4 18:31:58 discovery: waiting for other nodes:
error connecting to https://discovery.etcd.io, retrying in 4s
```

After this PR:

```
22:20:25 etcd2 | 2015/08/4 22:20:25 discovery: error #0: client: etcd
member https://discovery.etcd.io returns server error [Gateway Timeout]
22:20:25 etcd2 | 2015/08/4 22:20:25 discovery: waiting for other nodes:
error connecting to https://discovery.etcd.io, retrying in 4s
```

Conflicts:
	client/client.go
2015-08-21 14:55:35 -07:00
..
2015-06-15 18:18:50 -04:00
2015-06-15 18:18:50 -04:00
2015-06-03 10:02:37 -07:00
2015-04-17 10:57:01 -04:00
2015-04-06 13:49:43 -07:00
2015-04-17 10:57:01 -04:00
2015-04-17 10:57:01 -04:00