Fix upstream_cfg_prepend loop to put every element on a dedicated line

Hi James,

this tiny change will fix the upstream template. Turns this
```
check interval=3000 rise=2 fall=5 timeout=1000 type=http;  check_http_expect_alive http_2xx;  check_http_send "GET /_version HTTP/1.0\r\n\r\n";
```
into

```
check interval=3000 rise=2 fall=5 timeout=1000 type=http;
check_http_expect_alive http_2xx;
check_http_send "GET /_version HTTP/1.0\r\n\r\n";
```

Thanks a lot for your work on this module.

Cheers!
Daniel