Pass to the pre-hook the components to run

The pre-hook can implement a deployment policy if it receives the list of components that are being dispatched.  In this form, it receives a JSON object with a single field, "components", which contains a list of structures with the component names, like this:

```json
{
    "components": [
        {"name":"spma"},
        {"name":"accounts"}
    ]
}
```

This way I can extend the "API" in backwards-compatible ways in the future.