Fix Rust tests via lit on osx

[RustanLeino]

• Change the hack

  %exits-with 101 "%S/cargotest-rust/cargo" test
  

  to

  cd "%S/cargotest-rust" ; %exits-with 101 %cargo test
  

  in five test files related to Rust.

• Fill in definitions for %rm, %mv, and %cargo.

• Fix a missing " in a RUN command

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

[RustanLeino]

Unfortunately, this didn't work on CI:

An error occurred trying to start process 'cd' with working directory