Add simple printout from mysqlslap.test to avoid empty result file

mysql-test/r/mysqlslap.result

-# this test result intentionally blank due to running in silent mode.
+Test completed

mysql-test/t/mysqlslap.test

@@ -6,3 +6,5 @@
 --exec $MYSQL_SLAP --silent --drop-schema --concurrency=5 --concurrency-load=5 --iterations=20 --number-rows=10 --query="select * from t1" --data="INSERT INTO t1 VALUES (1, 'This is a test')" --create="CREATE TABLE t1 (id int, name varchar(64))"
 
 --exec $MYSQL_SLAP --silent --drop-schema --concurrency=5 --concurrency-load=5 --iterations=20 --delimiter=";" --number-rows=10 --query="select * from t1;select * from t2" --data="INSERT INTO t1 VALUES (1, 'This is a test'); insert into t2 values ('test', 'test2')" --create="CREATE TABLE t1 (id int, name varchar(64)); create table t2(foo1 varchar(32), foo2 varchar(32))"
+
+echo Test completed;