Supervisor logs fallback in get_supervisor_logs didn't work properly
because the exception was caught in api_process_raw instead. This was
not discovered in tests because the side effect raised OSError, which
isn't handled there.
To address that, I split the advanced_logs to two functions, one being a
wrapped API handler, one being plain function returning response without
any additional error handling. The tests now check for both cases of
errors (HassioError and random generic Python error).
Refs #5021
18d9d32bca