examples/scheduler/schedulers.sh: add error message

examples/scheduler/schedulers.sh

@@ -23,7 +23,7 @@ check_success()
     fi
 }
 
-[ -x ./cholesky/cholesky_tag ] || exit 77
+[ -x ./cholesky/cholesky_tag ] || (echo "Application ./cholesky/cholesky_tag unavailable" && exit 77)
 
 SCHEDULERS=`STARPU_SCHED="help" ./basic_examples/hello_world 2>&1 | awk '/\t->/ {print $1}'`