rtsp-client/rtsp-media: Adjust error code before sending request response
Issue: There is no way for an application to control what response is sent to a request when rtsp-client encounters an error while setting up the pipeline.
Solution: Store the errors reported from the medias pipeline in rtsp-media. Also add a virtual function in rtsp-client which, if overriden by the application will be called before sending the error response. There should be no change in todays behaviour unless this method is overriden.