fix sporadic failures of perfschema.privilege_table_io

it used to fail if main.create_drop_role was run before it

mysql-test/suite/perfschema/r/privilege_table_io.result

@@ -12,6 +12,7 @@ optimize table mysql.host;
 optimize table mysql.user;
 optimize table mysql.db;
 optimize table mysql.proxies_priv;
+optimize table mysql.roles_mapping;
 optimize table mysql.tables_priv;
 optimize table mysql.procs_priv;
 optimize table mysql.servers;

mysql-test/suite/perfschema/t/privilege_table_io.test

@@ -18,6 +18,7 @@ optimize table mysql.host;
 optimize table mysql.user;
 optimize table mysql.db;
 optimize table mysql.proxies_priv;
+optimize table mysql.roles_mapping;
 optimize table mysql.tables_priv;
 optimize table mysql.procs_priv;
 optimize table mysql.servers;