MB-6726: add config with rebalance_moves_before_compaction=256

Change-Id: I21d9e116acb56ec3498edd540c6e5191fca72b4a
Reviewed-on: http://review.couchbase.org/24605
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>