In order to be able to upgrade a server, a method is
  developed to bring a server off line. It does the following:
  
  - Gracefully force connected clients to disconnect 
  except the clients with SUPER privilege.
  
  - Allow super users to connect to manage the system.
  
  - Deny any other user access to the system.
  
  - Allow the replication slave thread to keep applying data to the server.