Display error on service commit involving closed connections

[JohannesGarm]

If you attempt to commit a service with a diff involving a device with a closed connection, you currently get this message:

Jun 4 12:39:48.172123: transaction_notification_handler: pid: 456561 Transaction 19 failed: Timeout waiting for remote peer Failed

A clearer message stating that there was no connection to the device would be better. The error message also takes a while to resolve, when it should be trivial to check whether there is an open connection to the device.