[EC2] Cleanup Python parens and disk dict

Minor fixes:
* Remove unnecessary parens (Python style)
* Sort `disks_by_instance` dict and remove duplicate `t1.micro` key
This dictionary had a duplicate key, `t1.micro`. To make it easier to prevent this kind of mistake again, I sorted the keys. This is how they appear on the [source page](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html), too.