- In MySQL Server 5.7 the mutex and condition was refactored into
  three layers of mutex types available from mysys. This caused all
  ndbcluster code using pthread_mutex_t to start using the
  native_mutex_t instead. This change causes merge conflicts all the
  time and also makes it impossible to use for example
  the safe_mutex functionality which can help find cases where
  dependent locks are held or not.
- Fix by changing to use mysql_mutex_t in ha_ndbcluster.
  The mutexes will not be performance schema instrumented at this
  time.
- Move mutex initializers in Ndb_index_stat_thread and Ndb_util_thread
  which are "static global" to do_init() so that they are created after
  the safe mutex functionality is initialized. Corresponding
  change to deinit function.