Send freeze frames via diagnostic_injector

Adds support to diagnostic_injector.py for reading freeze
frame data from JSON and generating a VehiclePropValue that
can be sent via vhal_emulator.

Add a freeze frame to diagjson.example for testing.

Test: ./diagnostic_injector.py ./diagjson.example
Change-Id: I74e8b27bae14ec194e4fa080f0ab467a97edb84b
2 files changed