[libvirt] Add virt-sandbox -s inherit, to execute the sandbox with parents label

This will allow us to run sandbox as the calling process, If I am running a shell as staff_u:unconfined_r:unconfined_t:s0, and I execute virt-sandbox -c lxc/// -- /bin/sh The second patch fixes a problem when users try to upgrade Generic Containers. [sandbox PATCH 1/2] Add virt-sandbox -s inherit, to execute the [sandbox PATCH 2/2] GenericContainers do not have unit files.