Public IP association support for launch configurations

Update to support the VPC specific AssociatePublicIpAddress property for launch configurations. I wasn't sure on the parameter names or output formatting, so apologies if that does not match conventions.

http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_CreateLaunchConfiguration.html
http://docs.aws.amazon.com/AutoScaling/latest/APIReference/API_DescribeLaunchConfigurations.html