virt-libvirt: Add virsh function for virsh cpu-stats

Signed-off-by: Kyla Zhang <weizhan@redhat.com>
virt-libvirt: Add test for virsh cpu-stats

The checkpoint including

1. When option = 'total'
   Displayed Total cpu_time >= User + System cpu_time
2. When option = 'start' or 'count'
   a. Displayed CPU's == Expected CPU's
   b. Cgroup cpu_time* >= sum of cpu_time of each cpu's displayed
3. When option has a combination of 'start', 'count', 'total'
   All the above conditions 1 & 2 are checked.
4. When option is None
   a. Displayed Total cpu_time >= sum of cpu_time of all cpu's displayed
   b. Pass condition when option = 'total' (1) is checked.

Signed-off-by: Kyla Zhang <weizhan@redhat.com>
virt-libvirt: Add configuration for virsh cpu-stats

Signed-off-by: Kyla Zhang <weizhan@redhat.com>
virt-libvirt: Skip cpu-stats on old libvirt

Signed-off-by: Chris Evich <cevich@redhat.com>