Support SHOW TABLE STATUS FROM db type queries in vtgate

[aquarapid]

In current Vitess, we support I_S passthrough for SHOW TABLE STATUS LIKE 'table1' in the context of the currently USE-ed database.

However, some MySQL introspection/workbench type tools (e.g. DBeaver) use the format:

SHOW TABLE STATUS FROM db1 LIKE 'table1'

This is just passed through by vtgate; and causes problems because the underlying shard instance knows the database (probably) as vt_db1, not db1. We should rewrite this query, since we already virtualize other introspection commands like SHOW FULL COLUMNS FROM db1.table1 (which does work).

Sample error returned from vtgate:

mysql> SHOW TABLE STATUS FROM db1 LIKE 'table1';
ERROR 1049 (42000): vtgate: http://localhost:15001/: target: db1.0.master, used tablet: zone1-100 (localhost): vttablet: rpc error: code = InvalidArgument desc = Unknown database 'db1' (errno 1049) (sqlstate 42000) (CallerID: userData1): Sql: "SHOW TABLE STATUS FROM db1 LIKE 'table1'", BindVars: {}