Re-add old owners in the pending CH when a node leaves during rebalance

Say we have a distributed cache [A, B] with numSegments = 1 and numOwners = 2. The initial topology is T: currentCH = {0: A B}, pendingCH = null

C joins, and A starts a rebalance. The topology is now T + 1: currentCH = {0: A B}, pendingCH = {0: A C}

C now leaves, A updates the consistent hashes to remove it with a new topology _T + 2: currentCH = {0: A B}, pendingCH = {0: A}

A doesn't need to receive any data, so the rebalance ends and the pending CH is installed as the current CH in topology T + 3: currentCH = {0: A}, pendingCH = null

This algorithm is relatively easy to follow and implement, but it does result in reduced availability of the cache data. It would be better if topology T + 2 could re-add B as an owner in the pending CH.