Show all databases with schemarouter in GUI

The GUI uses multiple queries to information_schema to build up the list of databases. As these queries are not handled by the schemarouter like SHOW DATABASES is, the GUI will only show the databases of the node that the query ended up on.

To solve this problem, the schemarouter would have to query the contents of the required information_schema tables, store it, parse the SQL the client requests and then generate a result that matches that query. In practice, this means either full cross-shard query support or at least partial support for a very limited set of SQL queries.

Maxscale GUI not show all databases in the query editor.

Maxscale GUI use information_schema.schemata.

Schemarouter use "show databases",
maybe there is currently some incompatibility.