Add a ghost unit right after deploying a service.
Merge pull request #301 from frankban/unplaced-unit

This is a follow up of Rick's work on this feature.
See https://github.com/juju/juju-gui/pull/299

QA:
- make devel;
- use `:flags:/mv/il/`;
- deploy a service;
- switch to machine view: you should se an unplaced unit/0 for that service.