Suppress varz jetstream output if not enabled

[matthiashanel]

Signed-off-by: Matthias Hanel [email protected]

What it used to look like:

  "jetstream": {
    "config": {
      "max_memory": 0,
      "max_storage": 0
    },
    "stats": null
  },

What this will be now

"jetstream": {},

Test

> nats-server -m 5222 &
[1] 84077
[84077] 2021/03/15 16:02:38.676376 [INF] Starting nats-server
[84077] 2021/03/15 16:02:38.676616 [INF]   Version:  2.2.0
[84077] 2021/03/15 16:02:38.676627 [INF]   Git:      [not set]
[84077] 2021/03/15 16:02:38.676737 [INF]   Name:     NDQKXZJBFFVO3XUIWIEXVBI3CWTDIIT3PP7DORBGNCG5Y5UZQB4FHQQN
[84077] 2021/03/15 16:02:38.676747 [INF]   ID:       NDQKXZJBFFVO3XUIWIEXVBI3CWTDIIT3PP7DORBGNCG5Y5UZQB4FHQQN
[84077] 2021/03/15 16:02:38.678096 [INF] Starting http monitor on 0.0.0.0:5222
[84077] 2021/03/15 16:02:38.678295 [INF] Listening for client connections on 0.0.0.0:4222
[84077] 2021/03/15 16:02:38.679013 [INF] Server is ready
> curl http://localhost:5222/varz | grep jetstream
 % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                Dload  Upload   Total   Spent    Left  Speed
100  1219  100  1219    0     0  87071      0 --:--:-- --:--:-- --:--:-- 87071
 "jetstream": {},
>

[derekcollison]

LGTM - Thanks.