Automate endpoint hogwash needed for running with latest AWS Java SDK

Latest version of AWS Java SDK required passing region or use custom endpoints file for some Walrus and S3 calls. We already have endpoints sample file in the repo. This change will automatically update that file with the EC2 and S3 endpoints from eucarc (which is required to run test anyway). This also adds a parameter to the build script such that an endpoint file can be specified (defaults to the bundled one)