All provider specific settings have been moved to the
provider section. The image name itself is now located
at the top level and called "name". It is required for all providers.
S3 images can now be bootstrapped outside EC2.
However, this fix adds the requirement of a "region" setting.
At some point we could make "region" optional and fail when bootstrap-vz
is run outside EC2 and no "region" is set.