MB-100: add rebalance configs with scheduler threads

Change-Id: If5c0bc507710179a2aeb3195e4aaec05a646d746
Reviewed-on: http://review.couchbase.org/24088
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>