Automate Location Asset S3 Bucket Creation

I created a story a while back for this but it was more specific to documentation rather than automation. @variousred there is code around creating a bucket if it doesn't exist for a location on deploy, but that depends on it's config var having already been set...which never currently happens programatically.

This creates a bucket and sets the config var in heroku during client import/update. You can now also call Location.create_asset_bucket to create a bucket for already imported clients...

https://www.pivotaltracker.com/n/projects/877197/stories/74730414
what about the location urn here for consistency — rather than a securerandom? I kind of feel like this operation should be idempotent, or be callable to determine what the asset bucket name was set as