AMQP exchanges and bindings are per-connection, lost on disconnect

[dborovcanin]

Exchanges and bindings are stored in per-channel maps (ch.exchanges, ch.bindings) in amqp/broker/channel.go. When an AMQP connection closes, all exchange and binding state is lost. In standard AMQP 0.9.1, durable exchanges and bindings survive connection and broker restarts. Clients must re-declare everything on every reconnect.