Simulates reblancing on a single scale-out involving simultaneous
addition of multiple nodes per rack.
Default parameters create a cluster with 2 racks, 70 tables, 256
tablets/table, 10 nodes, 88 shards/node.
Adds 6 nodes in parallel (3 per rack).
Current result on my laptop:
testlog - Rebalance took 21.874 [s] after 82 iteration(s)