make JSON output compatible with jq (for action:get among others)

**Is your feature request related to a problem? Please describe.**
When you `action:get`, you get the action's name printed before the JSON API response.
```
> ./bin/run runtime:action:get foo
foo
{ ... }
```

This makes the output incompatible with `jq` to project some subset of the values of interest. Since `aio` here diverges from `wsk`'s output of "ok: got action foo", perhaps do it better by dropping the action name that's currently prefixing the JSON response.

**Describe the solution you'd like**
```
> ./bin/run runtime:action:get foo
{
"annotations": [
{
"key": "exec",
"value": "nodejs:10"
}
],
"exec": {
"kind": "nodejs:10",
"binary": false
},
"limits": {
"concurrency": 1,
"logs": 10,
"memory": 256,
"timeout": 60000
},
"name": "foo",
"namespace": "guest",
"parameters": [],
"publish": false,
"version": "0.0.1"
}
```

**Describe alternatives you've considered**
Wrap the cli with another bash script.

Reproduisez `./bin/run runtime:action:get foo` et inspectez le point d’entrée `action:get` qui produit la sortie. C’est terminé lorsque la commande émet uniquement du JSON valide, sans le préfixe du nom de l’action, afin que sa réponse puisse être directement envoyée vers `jq`.

Rédigé par le modèle d'indexation à partir du texte de l'issue.