ISSUE-733: Producer can not reconnect to broker after server restart

[sijie]

Original Issue: apache#733

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Expected behavior

Producer reconnect to broker after server restart.

Actual behavior

In the current code, I find that if a connection is closed, it will try to stop all producer listeners and consumer handlers registered on it. But if the producer has set the connection to conn and does not register the listener to this connection in https://github.com/apache/pulsar-client-go/blob/1df5596aa7a351c6f43edb53f54b2a14b83b0073/pulsar/producer_partition.go#L264-L265. And the connection is closed by another goroutine because of connection.handleSendError https://github.com/apache/pulsar-client-go/blob/1df5596aa7a351c6f43edb53f54b2a14b83b0073/pulsar/internal/connection.go#L793. The producer can not do reconnectToBroker because no signal will sent to connectClosedCh.

Maybe we should check the result of RegisterListener and call ConnectionClosed by manually?

Steps to reproduce

It's not stable to reproduce

System configuration

Pulsar version: 0.7.0