long-running memory test that covers latest JRuby changes in stable

There are some fairly drastic changes to our management of JRuby in the stable branch. The most important one is the introduction of the new `max-requests-per-instance` setting, which causes JRuby instances to be flushed after they've handled a certain number of requests.

We need to do some long-running memory testing of a build that includes those changes, prior to shipping.