Changes to support XEN shared nodes and guest snapshots.
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.