patches: libvirt: Use "libvirt" unix_sock_group

patches: libvirt: Use "libvirt" unix_sock_group

Now that libvirt 3.6 is used on kvm nodes (via UCA repos), which
by default uses "libvirt" group for socket ownership,
change old "libvirtd" in salt-formula-libvirt's:
- libvirt/files/libvirtd.conf.Debian

This allows us to remove the manual group creation from VCP state
file, which was not re-entrant (failed if group already existed).

Change-Id: Id61fecd82daec1c0716ff4796b79dce47d096c3a
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>