Support termination policies in aws auto scaling group

[See AWS Auto Scaling Group Termination Policies](http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/AutoScalingBehavior.InstanceTermination.html)
Provide a way to set the termination_policies for an auto scaling group in aws
Note that this only allows for providing this attribute while creating the auto scaling group. 
I havent change the behavior for update (still only checks for max size, min size, desired capacity), 
read or delete