Alter Element._cache_artifact so it uses the virtual directory system

Background

At the moment, Element._cache_artifact exports files from the Sandbox's virtual directory to a real file system, creates some other directories around it, and adds in logs and other metadata YAML files, and then creates an Artifact from that directory.

We should be able to do all this using the virtual directory system, possibly writing the metadata and logs to a real directory then importing that into the new virtual directory, thus avoiding having to extract the majority of the artifact and recreate it.

Task description

• Modify _cache_artifact to use the virtual directory system.

Acceptance Criteria

Equivalent functionality verified by a remote execution test.

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assigned to @jmacarthur

This has raised some interesting issues with symlinks again. I have an implementation good enough to build freedesktop-sdk, but it fails our unit tests.

mentioned in merge request !991 (merged)

Currently stalled as there are some good questions being raised about how we handle symlinks in general. I'm going to raise a separate issue/MR to address the symlink issue and link it with this.

added Doing label

added To Do label and removed Doing label

marked this issue as related to #830 (closed)

closed via merge request !991 (merged)

mentioned in commit ef85e3b2