Fix machine token icon rendering issues

Placed token icons do not render properly under multiple situations. This fixes the following issues:

 - Switching away then back to mv fixes the machine token rendering issues but only renders the root container and unit.
 - Machine token doesn't get updated to show the units on deploy.
 - Root container doesn't get updated properly on deploy wrt placed units.

Persisting issues - These issues will not be resolved until a refactor of the token rendering code post 1.0:
- Container tokens disappear when deployed then reappear with the unit token properly rendered.
- Unit icons in the machine tokens disappear then reappear a few seconds later with the ack from juju.
I'd like to see a matching test for the removing of a unit on a machine as well please.