[Meta] Object Storage Configuration for RC1

[arschles]

This is a top level issue for improving object storage configuration in the v2.0-RC1 milestone

• Modify all components to use the objectstorage.toml/deis-objectstorage-secret.yaml files for object storage configuration.
  • deis/builder: Use deis-objectstorage-secret.yaml to get S3 credentials builder#224
  • deis/slugbuilder: Use deis-objectstorage-secret.yaml to get S3 credentials slugbuilder#32
  • deis/slugrunner: Use deis-objectstorage-secret.yaml to get S3 credentials slugrunner#18
  • deis/postgres: Use deis-objectstorage-secret.yaml to get S3 credentials postgres#71
  • deis/charts: feat(storage): add details for the builder and database buckets charts#171
  • deis/registry: fix(storage): make changes to support the object storage secret registry#31
  • deis/controller: feat(slugrunner): pass storage parameters to slugrunner controller#535
  • deis/dockerbuilder: feat(storage): Add support for all storage backends dockerbuilder#41
• Add the ability to specify the following 3 buckets in objectstorage.toml:
  • database_bucket - the bucket that the database should back up to
  • change bucket to slug_bucket - this is the bucket that the builder, slugbuilder, and slugrunner should use to pass tarballs and slugs between each other
  • registry_bucket - the bucket that the registry should save image layers to
• Change object storage documentation to show how to configure object storage with the single deis-object-storage-secret.yaml based method (Change object storage documentation to indicate how to configure object storage using unified configuration method workflow#99)