rv: improved shutdown check

cmd/rv/main.go

@@ -219,6 +219,8 @@ func run(rv *revid.Revid, ns *netsender.Sender, l *logger.Logger, nl *netlogger.
 			if err != nil {
 				l.Log(logger.Error, "could not power off", "error", err)
 			}
+		} else if _, ok := vars["Off"]; !ok {
+			l.Log(logger.Info, "Off variable has not been found")
 		}
 
 		// Configure revid based on the vars.