Feature/fog provider aws support

This is the first version of AWS support for the `fog_provider` plugin. For EC2 classic, you must specify the security_groups under Advanced (use default, if you don't know). For VPC, you must specify the security_group_ids, subnet_id, and allocate_public_ip under Advanced. Fixes #22 
Not yet... I can remove it, but it takes an IAM profile object and gets the human-readable name from it. At some point, I figure that we'll need it. It is a straight copy from `knife-ec2`, so it's easy enough to add back, later.