bug#27242: Fail to load LUKS encrypted rootfs, attempts to open luks device before it's ready.

[Adam Van Ymeren]

On my machine when booting GuixSD, it fails to find the rootfs from the
initramfs.  It errors out attempting to find the luks device node.
Shortly after it errors is when I see the kernel dmesg output of the
nvme0 device becomining ready.

It looks like we need to wait for the device node to become ready, or
poll/sleep a few times if we fail to locate the device.

Thanks!
-Adam