feat(start/stop): allow starting or stopping > 1 unit at a time

Changes our API and use to allow starting or stopping units as a group. `deisctl start|stop platform` now submits units in groups and then separately polls for their target status, which critically allows the services to start more or less in parallel rather than one-by-one.

Also implements `deis stop platform` as a blocking operation.
It only matter for `logger`, because the container must be present for controller to start due to the `--volumes-from`.  Once we remove that coupling order won't matter at all. :)