sqlsmith: handle user-defined schemas

[rafiss]

sqlsmith only looks for tables in the public schema. With the the 20.2 release, it should also look in user-defined schemas.

See

cockroach/pkg/internal/sqlsmith/schema.go

Lines 211 to 228 in 991893b

	func (s *Smither) extractTables() ([]*tableRef, error) {
	rows, err := s.db.Query(`
	SELECT
	table_catalog,
	table_schema,
	table_name,
	column_name,
	crdb_sql_type,
	generation_expression != '' AS computed,
	is_nullable = 'YES' AS nullable,
	is_hidden = 'YES' AS hidden
	FROM
	information_schema.columns
	WHERE
	table_schema = 'public'
	ORDER BY
	table_catalog, table_schema, table_name
	`)