test_singletonByClusterLeadership_withLeaderChange MUST work when down(self) is issued

[ktoso]

Expected a node to be down but it wasnt.

New type of issue there, will investigate.

out.txt

[ktoso]

Heh, simple one; from the "shutdown when being downed".

If we shutdown immediately, and the gossip does not make it "out" to others, then the others will not notice we're down.

By default, today, we do not have auto downing, thus down(self) in face of "shutdown on downing" leads to not notifying any nodes about it.

The workaround:

            // Take down the leader
            // first.cluster.down(node: first.cluster.node.node) // FIXME: must also work when the node downs itself and shuts down (!!!) (we do not move to down currently, no default downing impl)
             second.cluster.down(node: first.cluster.node.node)

And I'll work on making leaving() a thing now so we can always cluster.leave() which will wait for the gossip to spread the info.

[ktoso]

(i.e. this "works", but the fixme must be addressed, but not blocking the #375 PR)