guest-lvm-tape now writes 3 files to the tape for each guest operating system that it backs up.

A file that contains snapshot information for the guest OS lvm disk.
An xml file  from the guest that can be used to reconstruct the guest OS.
The gzipped snapshot of the guest OS disk.
Fixes bug in virsh.rkt.

System returns #t on success. The dump-xml clauses where backwards.