fix return database name

[hellobob]

The client got the wrong database name

[harshit-gangal]

@hellobob I think there should be a better way to provide database name to sharding-jdbc. I have not looked into the details of this framework. But current approach looks hackish to me.

[sougou]

We need to find a longer and more stable solution for this problem. The vt_ is itself a default that can be changed using init_dbname_override. We should look at prioritizing the project to move this metadata into the shard record.

[systay]

Issue #6753

[deepthi]

Superseded by #6791