* gnu/system/vm.scm (qemu-image): Use (guix build linux-initrd). Remove
'mknod' calls; use 'make-essential-device-nodes' to populate /dev on
the target image.
* gnu/packages/linux-initrd.scm (qemu-initrd): When /root/dev exists,
don't call 'make-essential-device-nodes'.
* gnu/packages/linux-initrd.scm (qemu-initrd): Add (guix build utils) to
#:modules, and use it. Copy .scm and .go files to /root.
* guix/build/linux-initrd.scm (bind-mount): New procedure.
* gnu/packages/linux-initrd.scm (qemu-initrd): Add #:modules argument.
Factorize and move some of the code to...
* guix/build/linux-initrd.scm: ... here. New file.
* Makefile.am (MODULES): Add it.