[packaging][uninstall] Uninstall command should also uninstall zones

[smklein]

Note: This issue tracks follow-up work from #686

omicron-package uninstall currently uninstalls all services, but does not yet uninstall zones. Instead, it relies on the "next boot of the sled agent" to remove them.

Having the packaging tool disable zones would actually be doable, with the following:

• Refactor the halt_and_remove code from src/illumos/zone.rs into a location accessible across other Omicron packages
• Query for omicron-owned zones within the packaging tool
• Invoke halt_and_remove on those zones

[bnaecker]

Closed by #909