Adjust logging of gossip errors to make it less annoying.

[ChillFish8]

Currently, if you have a cluster of nodes in Chitchat, and a node dies, each time chitchat attempts to gossip with the node you'll have a fairly vague error logged each time, which leads to a lot of unhelpful logs being repeated over and over until the node re-joins the cluster.

A possible solution would be to make the error returned by the Transport trait, more verbose so we can distinguish between a disconnect or not and not log the error if it's a node we already know is dead.