aim is to:
  a) if set_connect_timeout called, timeout connect attempt (for retry on
  next call) after timeout period
  b) preserve existing blocking behaviour otherwise (for, e.g. mgmapi)
  
  Related to customer issue with long time deleting ndb_cluster_connection
  object. believe we're hanging on the connect(2) call until timeout (when
  we then realise we should exit the thread).