message: add rust-src to the test environment
diff: @@ -8,6 +8,8 @@ RUN apt-get update && \
  # Install Rust toolchain
  RUN curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain nightly --profile minimal
  +RUN /root/.rustup/bin/rustup component add rust-src
  +RUN /root/.rustup/bin/rustup component add llvm-tools-preview
  RUN /root/.cargo/bin/cargo install cargo-download
  RUN /root/.cargo/bin/cargo install uhyve
  