info: improve handling of empty Info
info: improve handling of empty Info

Before this change, the function could print an error in some cases, for example;

```bash
docker -H tcp://127.0.0.1:2375 info --format '{{.LoggingDriver}}'

template: :1:2: executing "" at <.LoggingDriver>: reflect: indirection through nil pointer to embedded struct field Info
```

With this patch applied, the error is handled gracefully, and when failing to
connect with the daemon, the error is logged;

```bash
docker -H tcp://127.0.0.1:2375 info --format '{{.LoggingDriver}}'
Cannot connect to the Docker daemon at tcp://127.0.0.1:2375. Is the docker daemon running?

docker -H tcp://127.0.0.1:2375 info --format '{{json .}}'
Cannot connect to the Docker daemon at tcp://127.0.0.1:2375. Is the docker daemon running?
{"ID":"","Containers":0,"..."}}
```

Note that the connection error is also included in the JSON `ServerErrors` field,
so that the information does not get lost, even if STDERR would be redirected;

```bash
docker -H tcp://127.0.0.1:2375 info --format '{{json .ServerErrors}}' 2> /dev/null
["Cannot connect to the Docker daemon at tcp://127.0.0.1:2375. Is the docker daemon running?"]
```

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

docker/cli,cpuguy83/cli,docker/cli,thaJeztah/cli,thaJeztah/cli,cpuguy83/cli