Switched paths in S3 metadata to relative

[excitoon]

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Changelog category (leave one):

• New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Switched paths in S3 metadata to relative which allows to handle S3 blobs more easily.

[Akazz]

This changeset looks okay in general.

Although you might want to improve Metadata class in the future: to entirely encapsulate s3_root and return objectIds (which are simply random numbers) from addObject(). This way the class would be semantically more consistent and so you do not need to worry about generating names outside.

P.S. It looks like WriteIndirectBufferFromS3::finalize() is not exception-safe and can leak remote blob space (if metadata.save() fails). Perhaps it is worth putting a comment/TODO in about it.

[Akazz]

Performance tests failures seem unrelated completely.
fyi, @akuzm