Modify serial associator to use batch
https://fedorahosted.org/freeipa/ticket/1688
The serial associator is used to execute a command multiple times with different parameters. This is used for adding/removing a user into/from multiple groups. It has some issues:
Each command is executed one-by-one, so it could be slow.
* If there's a failure the rest of the commands will not be executed.
* This can be fixed by putting the commands into a batch and execute them at once.