Add rust_test and update TEST_MAPPING am: 479e43c4aa am: b98802d263 am: a6a8b939da

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-io/+/1365656

Change-Id: I3d04dc2b0b45d295fc0c89c9531857aeba45b349