TurnitinOC - improve error message when retrieving reports while connectivity to TII is down

If you disable your internet connection and run the queue job, the 'last_error' column is populated with your turnitin service url's host name (because a java.net.UnknownHostException is thrown, and the exception message is just the host name). The last_error message should be replaced with something more akin to "Failed to retrieve an originality score from Turnitin"