Create and use libvirtd group for package install

For the nova-kvm package install, we need to create the libvirtd group
and add the nova user to the group. This is because the element now uses
its own libvirtd.conf which is configured to use the libvirtd group.

Change-Id: Ic345b76a17ff75b468da8a493c6bf856d730a586
Merge "Create and use libvirtd group for package install"