[INLONG-265] Unexpected broker disappearance in broker list after updating default broker metadata

[dockerzhang]

It's a bug on 0.5.0 after migration of TUBEMQ-126: broker would disappear after updating its default metadata on unflushDataHold, which resulting an "out-of-sync" issue on metadata management.

Reproduce steps:

1. Bring a broker online;
2. Use webapi to submit an update about type of "admin_update_broker_configure", setting a new unflushDataHold;
3. Monitor log, it would successfully fire this event and proceed the update;
4. Refresh the broker list on master, you will find it's disappeared;
5. Retry to add the broker with the same BrokerID and IP Address, it would raise an error about duplicated configuration found, but the broker is still unseen in the broker list.

Bug is relating to BDB and Master initialization and meta-replication routines.

JIRA link - [INLONG-265] created by hystericalhell