- rewrite Ndb_global_schema_lock_guard into Ha_global_schema_lock_guard
  - add new handlerton->global_schema_func callback function
  - first make a list of hton's(since plugin_foreachi() is
    taking global mutex LOCK_plugin) and then calls the function outside
    of the mutex, this is similar to binlog_func_list which we
    hack into in 7.0