rust test: pass the remaining arguments through

The arguments after `rust test filename.rs` should be passed through
to the test binary. This allows the `rust` command to be used to run a
subset of tests, to run ignored tests, and to run benchmarks.
auto merge of #9213 : dcrewi/rust/rust-test-arguments, r=catamorphism

The arguments after `rust test filename.rs` should be passed through
to the test binary. This allows the `rust` command to be used to run a
subset of tests, to run ignored tests, and to run benchmarks.