Show tables fails on system tables.

[harshit-gangal]

mysql> use mysql;
Database changed
mysql> show tables;
ERROR 1105 (HY000): vtgate: http://harshit-X1:15001/: keyspace mysql fetch error: node doesn't exist: /vitess/zone1/keyspaces/mysql/SrvKeyspace

In mysqldump.

use mysql; implicitly calls show tables;