BDB HA - Group change thread-pool sized to availableProcessors +1

The BDB HA implementation internally uses a thread pool to process group change events. This thread pool is sized to Runtime.getRuntime().availableProcessors() + 1. On a machine with many cores, this will create a very large number of threads.

There is probably no reason why this thread pool needs to be quite so large. This problem does not cause a functional impact, but will consume more resources (threads + stack) than required.