Snitch name needs to be exchanged within cluster once, on shadow
round, so joining nodes cannot use wrong snitch. The snitch names
are compared on bootstrap and on normal node start.
If the cluster already used mixed snitches, the upgrade to this
version will fail. In this case customer needs to add a node with
correct snitch for every node with the wrong snitch, then put
down the nodes with the wrong snitch and only then do the upgrade.
Fixes#6832Closes#7739
b150906d39