[SSH Keys] keys-add doesn't display an error when an argument is missing

On `keys-add` command, when the `keyname` or the `path to the file`, it doesn't display any error. And it also still `exit 0` instead of `exit 1`.

```bash
$ scalingo keys-add ~/.ssh/yubikey.pub     
$ echo $?
0

$ scalingo keys-add test
$ echo $?
0
```

It should display an error and `exit 1`.
