Handle /proc/self/fd/N specially for kernel, bios and initrd.
Handle /proc/self/fd/N specially for kernel, bios and initrd.

This was already done for block device images, so reuse the same logic.

BUG=b:192256642
TEST=cargo test

Change-Id: Ifa69c0170ac39fc13eab61024d31e6ee5b2dd97c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3000986
Auto-Submit: Andrew Walbran <91a7c1b7f9f624e0ed1b099dc85ecb6025941ee9@google.com>
Reviewed-by: Chirantan Ekbote <35787c0e27de5c48735e07f8324823b765e8bcbc@chromium.org>
Commit-Queue: Andrew Walbran <91a7c1b7f9f624e0ed1b099dc85ecb6025941ee9@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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