[bitcoin/bitcoin] [zmq] pub/sub is not reliable at all (#12754)

@mruddy Just tried it out, got the same results — everything seems to still be connected and appear immediately (block #7, after a `generate 1` after 45 minutes, port 28332):

screen shot 2018-08-20 at 1 00 24 pm

Maybe this is a timeout due to a middle box topology, like you mentioned?