Provide ability to pass parameters as a JSON object on the command line

@l2fprod commented on [Wed Nov 16 2016](https://github.com/apache/incubator-openwhisk/issues/1513)

Just like I can pass the JSON body of a request on the command line with cURL, I'd like to be able to pass the parameters the same way with the OpenWhisk CLI

```
curl -H "Content-Type: application/json" -X POST -d '{"username":"xyz","password":"xyz"}' http://localhost:3000/api/login
```

as example:

```
wsk action invoke --body '{"key1": "value1", "object1": { "object1Prop": "anotherValue" }}'
```

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@mbehrendt commented on [Wed Nov 16 2016](https://github.com/apache/incubator-openwhisk/issues/1513#issuecomment-260885474)

good point.

should we even allow piping it in, sth like `echo | wsk action invoke myAction` ?

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@dubeejw commented on [Wed Nov 16 2016](https://github.com/apache/incubator-openwhisk/issues/1513#issuecomment-260973313)

You can put the JSON in a file, and pass that filename to the -P flag.

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@l2fprod commented on [Wed Nov 16 2016](https://github.com/apache/incubator-openwhisk/issues/1513#issuecomment-260973908)

true but here I don't want to have to create a temp file.