selftests/memory-hotplug: Adjust log info for maintainability

Redirect misleading error message to /dev/null for
offline_memory_expect_success(), And, add an output
for online->offline test.
Signed-off-by: Zhao Gongyi <zhaogongyi@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/memory-hotplug/mem-on-off-test.sh

@@ -207,8 +207,11 @@ echo -e "\t trying to offline $target out of $hotpluggable_num memory block(s):"
 for memory in `hotpluggable_online_memory`; do
 	if [ "$target" -gt 0 ]; then
 		echo "online->offline memory$memory"
-		if offline_memory_expect_success $memory; then
+		if offline_memory_expect_success $memory &>/dev/null; then
 			target=$(($target - 1))
+			echo "-> Success"
+		else
+			echo "-> Failure"
 		fi
 	fi
 done
@@ -267,7 +270,7 @@ prerequisite_extra
 echo 0 > $NOTIFIER_ERR_INJECT_DIR/actions/MEM_GOING_OFFLINE/error
 for memory in `hotpluggable_online_memory`; do
 	if [ $((RANDOM % 100)) -lt $ratio ]; then
-		offline_memory_expect_success $memory
+		offline_memory_expect_success $memory &>/dev/null
 	fi
 done