Output dictionary with error field

When an action outputs a dictionary with an `error` field, the other fields are dropped from the output dictionary, for example:

```
$ wsk action invoke /whisk.system/utils/echo -br -p statusCode 404 -p error foo -p message bar
{
"error": "foo"
}
```

This is confusing and forces the action programmer to carefully wrap and unwrap things like error codes. I would prefer all the fields to be preserved.

Start by reproducing the `wsk action invoke /whisk.system/utils/echo -br` example with `statusCode`, `error`, and `message` parameters, then trace where action results containing an `error` field are handled. Done means the output preserves `error` and the other fields, with a regression test covering this invocation.

Written by the indexing model from the issue text.