This allows the ec2 module to take advantage of additions to the Boto library that were introduced in 2.13.0. Specifically:
- When starting an instance in non-default VPC, AWS will not, by default, automatically assign a public IP address. On the UI, this a radio button option. Boto introduced this functionality in 2.13.0 (http://goo.gl/H9UN4a).
- Added a parameter to EC2 module, assign_public_ip to utilize the Boto functionality.
- If assign_public_ip is set to true, ensure that Boto version has the available functionality mentioned above.
- Also be sure that this new option is only used with vpc_subnet_id as it doesn't make sense outside of that context.