Properly propagate transfer issues

[JoeZiminski]

At the moment the transfer occurs on the rclone side and the user has to go and check the logs to see whether the transfer completely properlly. It would be much better to check the rlcone side (hopefully it can be made to return a code based on issues encountered in the error (nice)) or search the log file for any errors and propagate to the user (not nice). For example, it is currently confusing if the transfer fails due to a bad central path over SSH.