Nodes "changing identity" can prevents primary groups

Easier steps to reproduce:

1. Start 2 nodes cluster

2. Break network connectivity between nodes

3. Shutdown node 2

4. Bring the network up again

5. Start node 2

What happens?

1. When the network is down, both nodes go into non-primary. So node 1 sees node 2 as partitioned.

2. Node 2 shutdown. During the clean shutdown, gvwstate.dat file is deleted.

3. When Node 2 is started after the clean shutdown, its identity changes (no gvwstate.dat file

4. Node 1 sees Node 2 joining the cluster:

   1. gmcast layer detects that the identity changed

   2. evs layer does not keep this information

   3. pc layer is notified about node 2 joining with new identity, but it still keeps the old identity and things this node is partitioned. On this layer there is no link between old and new identity, so it does not know it is the same node

Solution: pc layer has to be notified about node identity change.

About "stop pxc-node3":

it used to reproduce fairly easily on 5.7 because nodes were aborting and shutting down when non-primary, which is apparently not that frequent in pxc 8.0 anymore.

Though, it still happens to get stopped in some productions due to automation (e.g puppet), manual restarts, if a SST got cancelled,  and probably for other reasons I am still searching.

So, this does not seem like a stretch to me to include this "stop"

Reproduction:

1. install regular pxc on docker

https://docs.percona.com/percona-xtradb-cluster/8.0/docker.html

With all the steps, no need any modification

2. break network

=> disconnect network on pxc node2 + node3

Then, after some time to let node1 go non-primary, reconnect node2. It will keep non primary

Alternative: reconnecting network at the same time on node2 and 3 would enable "merge quorum"

Stop node3, reconnect network, restart it

Alternative: just reconnecting network can enable merge quorum again in this case

All nodes will stay non primary

Now, restart node3 in loop will make it duplicated

nodes then won't forget about the last one, for some reason it's not cleaned:

Will do, working on it

Please provide steps to reproduce.