Add instance_id parameter to ec2_asg

Auto Scaling provides you with an option to create a new launch configuration using the attributes from an existing
Amazon EC2 instance. when you use this option, Auto scaling copies the attributes from the specified instance into a
template from which you can launch one or more Auto Scaling groups[1].

The boto library supports this with the boto.ec2.autoscale.group.AutoScalingGroup class[2].

[1] http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/create-lc-with-instanceID.html
[2] http://boto.readthedocs.org/en/latest/ref/autoscale.html#module-boto.ec2.autoscale.group