* gnu/system/vm.scm (qemu-image): Add 'populate' keyword parameter and
honor it; make it an input.
(/etc/shadow): New procedure.
(example2): Call it; build 'populate' script, and pass it to
'qemu-image'.
* 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/system/vm.scm (qemu-image): Add #:inputs-to-copy and
#:boot-expression parameters. Honor them. Append INPUTS-TO-COPY to
the #:inputs argument for `expression->derivation-in-linux-vm'.
(example2): Add #:boot-expression and #:inputs-to-copy arguments.
* gnu/packages/qemu.scm (qemu-kvm): Remove.
(qemu): Incorporate parts of QEMU-KVM that used to be inherited.
(qemu-kvm/smb-shares): Rename to...
(qemu/smb-shares): ... this.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Adjust
accordingly.