cargo xtest doesn't work under WSL1 with native QEMU

1. Install QEMU natively on Windows
2. Under WSL setup cargo
3. In ~/bin/qemu-system-x86_64 put exec /mnt/c/Program\ Files/qemu/qemu-system-x86_64.exe "$@" and make the file executable
4. run cargo xrun
5. run cargo xtest

The xrun command works because it provides a relative path to the target to run to qemu. However xtest fails because it provides an absolute path which native QEMU doesn't understand. Passing a relative path just like xrun does should fix the issue.

Running: `qemu-system-x86_64 -drive format=raw,file=/mnt/c/projects/blog_os/target/x86_64-blog_os/debug/deps/bootimage-blog_os-f9b6181f9decdfac.bin -device isa-debug-exit,iobase=0xf4,iosize=0x04 -serial stdio -display none`
C:\Program Files\qemu\qemu-system-x86_64.exe: -drive format=raw,file=/mnt/c/projects/blog_os/target/x86_64-blog_os/debug/deps/bootimage-blog_os-f9b6181f9decdfac.bin: Could not open '/mnt/c/open/blog_os/target/x86_64-blog_os/debug/deps/bootimage-blog_os-f9b6181f9decdfac.bin': The system cannot find the path specified.

Reproduce the issue under WSL1 with native QEMU using the documented cargo xrun and cargo xtest commands. Compare how xrun and xtest pass the target path to QEMU; done means xtest passes a relative path that native QEMU can open and the test command succeeds.