Add tests for virtio input device
Add tests for virtio input device

These tests would have caught chromium:939585

Test=cargo test -p devices

Change-Id: If980fe8b56b9d76e77b652fb727b8849dbedd9cc
Reviewed-on: https://chromium-review.googlesource.com/1512759
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Jorge Moreira Broche <dbc2f9dc0b0e21f6bd297b0a2dc4733f06f8a572@google.com>
Reviewed-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm