Improve ec2_instance_older_generation control

[graza-io]

Currently the ec2_instance_older_generation control is using a hard-coded list of out-dated instance families to check for: t2.% m3.% m4.%

Query

Ideally, once the region based changes are implemented for the table_aws_ec2_instance_type - we should be able to ascertain if an instance is out of date by using the current_generation column on this table.