RFR (T) 8237501: TestInstanceKlassSizeForInstance runs TestInstanceKlassSize instead

[coleen . phillimore]

Fix cut/paste error and reran the test, which passes.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8237501.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8237501

Thanks,
Coleen