Disclaim host init responsibilities.

This will no longer be the job of the main controller. For now,
we provide some shell scripts for common configuration. Using this
separatation of concerns everything is a lot cleaner and easier.

The non-essential strowger and shelf plugins are setup by their
respective plugins, which also creates some obvious opportunties
to manage those services through regular means.

The system deployment is now actually called "system", and can be
controlled like any other, moved around the cluster etc, as it no
longer contains the essential host services.

The upstart plugin only has to worry about managing regular services
and is thus a lot simpler.