Make BatchlogManagerMBean.forceBatchlogReplay() blocking

In 3.0, BatchlogManagerMBean.forceBatchlogReplay() blocks until completion. In 2.2 it just submits a runnable and instaexits, which makes it impossible to create non-flaky dtests that rely on batchlog replay.

here is a small 2.2-only commit that make the behaviour consistent between 2.2 and 3.0.