rwroot automatically adds root=/dev/vd[a-z], but the example image
actually uses /dev/vda5. This leads to confusion when two root= kernel
command line arguments are passed in and only one of them works.
Therefore we use rwdisk instead which doesn't add the kernel argument.
BUG=b:236198584
TEST=mdbook builds, examples build and run
Change-Id: I9bfc05445b1e2aef197a43ee647d7c784d50dad7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3708365
Commit-Queue: Yuanchu Xie <yuanchu@google.com>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>