invirt-admin create-sysvm

This produces a new sysvm with lvcreate, invirt-create-image,
and writing out a Xen config file.

invirt-admin will end up in a package, but which one I'm not sure,
so for now it's on its own.  Probably it should also end up being
written in Python rather than shell.

svn path=/trunk/scripts/invirt-admin/; revision=2040