Add `cargo-all-features`

[JonathanWoollett-Light]

Currently the rust-vmm CI runs carg test --all-features see:

rust-vmm-ci/.buildkite/test_description.json

Line 25 in 72ebeb3

"command": "cargo test --all-features --workspace",

This doesn't work for certain cases e.g. rust-vmm/vhost#218 (comment).

To test all features while supporting configuration for exclusive features unittests-gnu should run cargo test-all-features using https://github.com/frewsxcv/cargo-all-features.

[epilys]

An alternative to consider is https://github.com/taiki-e/cargo-hack which runs a cargo subcommand for different target environments and deduplicated feature combinations with the ability of excluding specific combos (e.g. for incompatible features).

[epilys]

Note for the future: If artifact storage size becomes a problem on CI because of running different feature sets, we could use https://github.com/holmgr/cargo-sweep to cleanup between runs.

[roypat]

fwiw, if we reduce this to just doing cargo check-all-features (under the assumption that tests are additive, and just doing cargo test --all-features is enough), then it finishes in a few minutes on vm-memory (which has a lot of features), so its definitely feasible (and I think would be very helpful once we sort out our mutually exclusive features)