Snapshots are done a little differently then openvz of course, since
there are potentially multiple disk partitions and a kernel. The basic
operation is:

1. Fire off reboot_prepare from boss. Changes to reboot_prepare result
   in the guest "halting" insted of rebooting.

2. Fire off the create-image client script, which will take imagezips
   of all of the disks (except the swap partition), and grab a copy of
   the kernel. A new xm.conf file is written, and then the directory
   is first tar'ed and then we imagezip that bundle for upload.

3. When booting a guest, we now look for guest images that are
   packaged in this way, although we still support the older method
   for backwards compatability. All of the disks are restored, and a
   new xm.conf created that points to the new kernel.