Better error message when aborting simulation

tools/cooja/java/org/contikios/cooja/Cooja.java

@@ -3279,7 +3279,7 @@ public class Cooja extends Observable {
             System.exit(1);
           }
         } else {
-          logger.fatal("No test editor controlling simulation, aborting");
+          logger.fatal("No plugin controlling simulation, aborting");
           System.exit(1);
         }
       }