Cleaned up backup/nfs recipes

Cleaned up some issues I found with the backup shell scripts that were occurring with long running backups when multiple databases were being backed up concurrently. Now it does them sequentially with a cleaner loop.

Ability to define which server(aggregator) will run the backup scripts, eventually this can be set by listing the aggregators and picking the master or a slave.

I added in the rotate-backups python script used to do the rotating.