fix client trying rapidly and repeatedly to connect to offline nodes

This adds a mechanism to prevent a re-handshake with an address which has failed to handshake within the last 60 seconds.

I see my nodes often making several connection attempts per second to the same address. Worse, they seem to sometimes get stuck in loops where they continually rediscover and try to handshake with a significant portion of the (offline) network.

This remedies those observations. Operations like contract republishing especially take much less time for me and I'm seeing on the order of a 70% drop in sent messages at certain times.