Change VM cgroup suffix from '{lxc,qemu}.libvirt' to 'libvirt-{lxc,qemu}'

Change VM cgroup suffix from '{lxc,qemu}.libvirt' to 'libvirt-{lxc,qemu}'

Recently we changed to create VM cgroups with the naming pattern
$VMNAME.$DRIVER.libvirt. Following discussions with the systemd
community it was decided that only having a single '.' in the
names is preferrable. So this changes the naming scheme to be
$VMNAME.libvirt-$DRIVER. eg for LXC 'mycontainer.libvirt-lxc' or
for KVM 'myvm.libvirt-qemu'.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>