gnu: vm: `qemu-image' can copy store closures into the target image.

* 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: `expression->derivation-in-linux-vm' accepts files as inputs.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Accept items
  in INPUTS that refer to a file instead of a package.

gnu: `expression->derivation-in-linux-vm' export references graphs.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Add
  #:reference-graphs parameter.  Honor it.  Delete duplicates in
  #:modules argument.

vm: Use more keyword parameters for `expression->derivation-in-linux-vm'.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Turn `system'
  and `inputs' into keyword parameters.
  (qemu-image, example1): Adjust accordingly.

gnu: Have `qemu-image' explicitly reboot when done.

* gnu/system/vm.scm (qemu-image): Call `reboot' when we're done.  Change
  `menuentry' title.

gnu: Remove QEMU-KVM, which is no longer needed.

* 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.

Add (gnu system vm).

* gnu/system/vm.scm: New file.
* Makefile.am (MODULES): Add it.

Add (gnu system vm).

* gnu/system/vm.scm: New file.
* Makefile.am (MODULES): Add it.