Partition versions contain duplicates

During an upgrade from 2.5.1 to 3.0.2 it can happen that the partition versions end up with a high number of duplicated entries.

It happened two times:

1. A 2 node 2.5.1 cluster adding a 3.0.2 node (which worked). Removing on 2.5.1 made the 3.0.2 node fail. It's unclear whether the partition version were wrong already when the 3.0.2 was added, or only when the 2.5.1 was removed.

2. A 5 node 2.5.1 cluster gets upgraded to 3.0.2 with a swap rebalance. The upgrade works fine for 4 nodes. The last rebalance of the 5th node makes trouble. It's also unclear where exactly the duplicated entries happen, but it can at least be seen on the last rebalance try.