When encountering errors, the Algorithm::read() function either uses LOG(Fatal) or throws exceptions from the boost property_tree functions. To prepare for replacing boost JSON parse with the YamlParser class, give the Algorithm::read() function the ability to return an error code, and propagate it all the way to the IPA module init() function. All algorithm classes return a hardcoded 0 value for now, subsequent commits will change that. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Naushir Patuck <naush@raspberrypi.com> Tested-by: Naushir Patuck <naush@raspberrypi.com>