DriverService will throw a WebDriverException if it cannot start the dri...

DriverService will throw a WebDriverException if it cannot start the driver process so now it's more easy to debug if there's same problem during the driver initialization . Previous behaviour was to silently fail so client code will get errors only later when it will try to use the driver istance.
note: i used WebDriverException to have a consistent behaviour with the java code
note2: i do also a simply validation on the 'status' response to manage the case where the failure is caused explicitly setting a port that is already use by an http server (so the 'status' command can return a valid http response)