node-proxy: update the JSON data structure

node-proxy: update the JSON data structure

Change the data structure from:
```
{
  "storage": "ok",
  "processors": "ok",
  "network": "ok",
  "memory": "ok",
  "power": "ok",
  "fans": "ok"
}
```
to:

```
{
    "host": "node1",
    "sn": "xxxx",
    "status": {
        "storage": {
        }
    }
}
```

In order to provide a unique key (sn) which is more reliable at the top
level of the dict.

Signed-off-by: Guillaume Abrioux <gabrioux@ibm.com>
(cherry picked from commit 65d3f781f92505eb708716eb281c670a71ed503c)