Graceful shutdown of MaxScale when using more than one MaxScale instance

The customer has to restart MaxScale in case of MaxScale upgrade or MaxScale maintenance (for example if MaxScale would start to take too many resources).

The task is to implement a graceful shutdown of MaxScale without causing any notable interruptions to users that uses MaxScale to connect to MariaDB server.

The logic would be as follows when requesting a graceful shutdown:

• Move all connections to the other MaxScale
• Shutdown MaxScale
• One restart, move half of the connections from the other MaxScale to the current one.

The customer can then repeat the above procedure with the other MaxScale if needed.