suppress sanitizer warning about (expected) leak

[comicfans]

to address https://github.com/ros/class_loader/issues/131, this didn't change code, instead it suppress the sanitizer report because we know this leak is expected. this suppression can't be done through runtime suppression file because sanitizer can't do that for dlopen shared libraries https://github.com/google/sanitizers/issues/89 , so better to annotate it.