First draft of ec2 implementation

https://twitter.com/solomonstre/status/476778223838035970

Docker-DCO-1.1-Signed-off-by: Aaron Feng <aaron.feng@gmail.com> (github:
aaronfeng)
I think if you're accepting tags, you should be accessing all instances with that tag.  I know you had a TODO below for the creation part, but I feel like addressing all things with that tag, rather than just the first is important to avoid some really nasty gotchas.