Run the node.js backend in Vagrant

Currently, the node.js sponsorship-form backend isn't actually launched in our Vagrant dev environment. This will run it right from the rsync'd `/vagrant_data/src/sponsorship-form` directory.

## Remaining Work

- [x] Verify that the "content" role works properly from `jenkins_push.yml` in a real deployment.
- [x] Run forever with `-w` in development mode, to pick up changes live.
- [x] Create a `script/formlogs` to tail the node.js process logs.

/cc @kenperkins, @ycombinator