Instead of asking blob store to create output for posting blob content, this change provides that content of the blob to the blob store for writing. This will significantly simplify the interface for S3 and Azure plugins.
Until now we had a cloud-aws plugin which is providing 2 disctinct features:
* discovery on EC2
* snapshot/restore on S3
This commit splits the plugin by feature so people can use either one or the other or both features.
Doc is updated accordingly.