Add engine_cfg to watchdog

Watch changes to engine config via watchdog. When the file is
modified, watchdog picks it up, verifies if the current engine
is disabled, and if yes, take steps in stop_engine(), to stop
the engine. That function is currently empty, will be filled in
in future commits

Change-Id: If3e2e952009f2f8a610459645c4403c77581e717
Merge "Add engine_cfg to watchdog"