[CV] Add a retry mechanism for adding nodes for the rebalance-in nemesis.

What's the problem?

On the rebalance-in (and perhaps the swap-rebalance) nemesis, there's a fixed sleep of 5 seconds which may not allow a sufficient period of time to pass before a node can be added back in.

Add some form a retry or wait mechanism for 'addNodes' such that we don't have to rely on the timing of the sleep for the rebalance-in nemesis.