[RUST][CI] Add rust frontend tests in Jenkins

[ehsanmok]

Per discussion #2318 required for frontend PR.

[ehsanmok]

@tqchen python frontend gpu error ?!

[tqchen]

@ehsanmok Given that we are a bit limited in CI resource, let us put the test script on the same stage as the normal rust test

[ehsanmok]

@tqchen I think normal (runtime) Rust doesn't need unpack_lib here whereas frontend Rust needs unpack_lib('cpu', tvm_multilib) (that's why the frontend PR build fails due to not finding libtvm_runtime.so). So if you want to make them all in the same test script, we can put runtime Rust where it has access to tvm_multilib and separate them when we have more resources later!

[tqchen]

That works