dual_asg cannot terminate launch configuration

In the dual_asg role, you're trying to:
1. delete the relative autoscaling group
2. then [get the name of the launch configuration](https://github.com/ansible/immutablish-deploys/blob/master/roles/dual_asg/tasks/terminate_relative.yml#L10) from the returned result and delete the launch configuration

The problem is that there is [no returned result](https://github.com/ansible/ansible-modules-core/blob/devel/cloud/amazon/ec2_asg.py#L465-L468) (and, [here](https://github.com/ansible/ansible-modules-core/blob/devel/cloud/amazon/ec2_asg.py#L465-L468)).

The bigger problem is that without that returned result from deleting the asg, there's no programmatic way to delete the lc -- remember, the name of the lc has a timestamp suffix.

How do we do this?

Start with roles/dual_asg/tasks/terminate_relative.yml and compare its expected deletion result with the referenced ec2_asg.py code at lines 465-468. Determine how the timestamped launch configuration name can be obtained after deleting the relative autoscaling group; done means both the group and its launch configuration are deleted reliably.

Written by the indexing model from the issue text.