Have spark-ec2 set EC2 instance names

spark-ec2 launches EC2 instances with no names. It would be nice if it gave each instance it launched a descriptive name.

I suggest:

spark-{spark-cluster-name}-{master,slave}-{instance-id}

For example, the instances of a Spark cluster called prod1 would have the following names:

spark-prod1-master-i-18a1f548
spark-prod1-slave-i-01a1f551
spark-prod1-slave-i-04a1f554
spark-prod1-slave-i-05a1f555
spark-prod1-slave-i-06a1f556

Amazon implements instance names as tags, so that's what would need to be set for each launched instance.