overlay support for mysql-test-run and mysqltest

mysql-test-run auto-disables all optional plugins.


mysql-test/include/default_client.cnf:
  no @OPT.plugindir anymore
mysql-test/include/default_mysqld.cnf:
  don't disable plugins manually - mtr can do it better
mysql-test/suite/innodb/t/innodb_bug47167.test:
  mtr now uses suite-dir as an include path
mysql-test/suite/innodb/t/innodb_file_format.test:
  mtr now uses suite-dir as an include path
mysql-test/t/partition_binlog.test:
  this test uses partitions
storage/example/mysql-test/mtr/t/source.result:
  update results. as mysqltest includes the correct overlayed include
storage/innobase/handler/ha_innodb.cc:
  the assert is wrong

mysql-test/include/mtr_check.sql

@@ -74,5 +74,8 @@ BEGIN
     mysql.time_zone_transition_type,
     mysql.user;
 
+  -- verify that no plugin changed its disabled/enabled state
+  SELECT * FROM INFORMATION_SCHEMA.PLUGINS;
+
 END||