Allow specification of other regions than us-east

[sooheon]

I just took a look at the possible args for create-site, and I don't see anything immediately referencing regions.

[martinklepsch]

@sooheon I think that option might be missing currently, I'll rename this issue to track that properly.

PR would be welcome if you feel like taking a stab at it. (Would probably also require some small changes to the generated CloudFormation template.)