This commits adds testing of libhermit-rs for pushes and PRs. Both debug and release builds are tested with 1 and 2 cores each.

Tests are done via the rusty-hermit demo in rusty-hermit. rusty-hermit is cloned and checked out to the devel branch. The demo is then compiled with the version of libhermit-rs that triggered the build and not the version specified as a submodule in rusty-hermit.

rusty-hermit including libhermit-rs is compiled fresh every time, but cargo dependencies such as uhyve and cargo-download are cached to speed up build time.