Allow bucket base dir in aws eb
Allow bucket base dir in aws eb

- Be able to upload to an S3 to a different path than the root

snap-ci/snap-deploy,alabeduarte/snap-deploy,tiarebalbi/snap-deploy,alabeduarte/snap-deploy,BognarB/snap-deploy,BognarB/snap-deploy,snap-ci/snap-deploy,tiarebalbi/snap-deploy