Summary:
This diff makes sure that devices will actually instantiate applicable sandy device plugins. Similar to how client plugins are owned by Client, device plugins are directly owned by BaseDevice, which significantly simplifies life cycle management and doesn't dispatch updates to all Redux connect components whenever something irrelevant changes.
Also made sure `device.teardown()` is called. That API already existed, but wasn't used or implemented before.
Updated Flipper test utils to support testing device plugins as well (both Sandy and classic ones)
Reviewed By: passy, nikoant
Differential Revision: D22693929
fbshipit-source-id: 73b2b8666ef7a0e748ea89360db84734d37eb5be
