normalize usage of @ignore and ProblemList

Although ProblemList and @ignore achieve the same end result (test exclusion), they serve different goals and have slightly meanings. Simplified, @ignore should be used to exclude useless or harmful tests, and ProblemList in all other cases (see yet-not-integrated `ProblemListing or `@ignore`-ing a Test` section of dev guide, PR -- https://github.com/openjdk/guide/pull/21 for more details).

Due to different reasons, this hasn't always been followed and some currently @ignore-d tests should rather be ProblemList-ed, and some of ProblemList-ed should be @ignore-d, this issue is to clean up the current state in a hope that this will reduce further confusion.

(this is a JDK-wide cleanup, filed against hotspot/test for the lack of a better component; actual cleanups are going to be done by subtask against corresponding component/subcomponent)