BUG#11132 Connections stuck in CLOSE_WAIT

In 4.1 (it is different in 5.0), we do not use the mgm connection after fetching the
configuration (and if we did, we would have to have calls to check the connection and
reconnect if needed - in case the mgm server had restarted) so we can disconnect after
first use.

This means we won't have connections stuck in CLOSE_WAIT when the mgm server shuts down.

ndb/src/common/mgmcommon/ConfigRetriever.cpp

@@ -139,6 +139,8 @@ ConfigRetriever::getConfig(NdbMgmHandle m_handle){
     return 0;
   }
 
+  ndb_mgm_disconnect(m_handle);
+
   return conf;
 }