feat(SwingSet): Support SLOG* environment variables when running tests

[gibson042]

Description

Provides a buildTestVatController test helper that wraps buildVatController in order to inject a slogSender option as requested by SLOGFILE/SLOGSENDER/SLOGSENDER_AGENT environment variables.

Security Considerations

Minimal; this is testing code and nobody will be looking for a slog file they didn't request. The worst plausible scenario I can think of is someone having an exported environment variable and being surprised that running tests unexpectedly affects a file.

Scaling Considerations

n/a

Documentation Considerations

This is already documented at docs/env.md, but perhaps the "Affects:" details should be updated to mention SwingSet tests?

Testing Considerations

This is currently limited to the file where I needed it, but could easily cover much more.

Upgrade Considerations

n/a

[mhofman]

Looks fine. I've always found it weird that buildVatController is "used for tests only", yet lives in src, but I think it's because some tools also use it.

[gibson042]

I've always found it weird that buildVatController is "used for tests only", yet lives in src, but I think it's because some tools also use it.

Hmm, I didn't realize that but you're right. Maybe I should instead skip the wrapper and add this functionality directly? I could probably also move the function to tools in the process.

[mhofman]

add this functionality directly? I could probably also move the function to tools in the process.

I think I'd only want to add it directly if moved. The reason is that the kernel source shouldn't take a dependency on the telemetry package.