Realistic Mock for test_device_update

[t-sasatani]

The current tests for device_update only test update functions and models, but we eventually want a more realistic Mock class that imitates device behavior.

• Step 1: Make a mock class that imitates the current update controller and have methods that just consume data like okDevMock.setWire. (Might not change test strength much because the current update controller is a one-way communication device and doesn't have response, but good to do anyways.)
• Step 2: Make an integrated mock class that does the entire process from command generation to confirming the update. This should be something like a class that accepts update commands and returns updated configurations through okDevMock.