MB-100: add vperf rebalance config with replica index

Change-Id: Ic3b61ea9760b52df37f56ea8c9502139087e0a5f
Reviewed-on: http://review.couchbase.org/27207
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>