Automate releases to Amazon S3

We are switching to Amazon S3 for OSv pre-built image releases.

The script uses S3cmd:

  http://s3tools.org/s3cmd

which can be installed on Fedora with:

  yum install s3cmd python-magic

Please remember to configure your Amazon S3 credentials before running
the script:

  s3cmd --configure

To release a new version of OSv:

  git tag <version>

  ./scrips/release-s3

  git push --tags

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>