qemuDomainSetNumaParamsLive: set nodeset for root cgroup

qemuDomainSetNumaParamsLive: set nodeset for root cgroup

This function handles the change of NUMA nodeset for a given
guest, setting CpusetMems for the emulator, vcpus and IOThread
sub-groups. It doesn't set the same  nodeset to the root cgroup
though. This means that cpuset.mems of the root cgroup ends up
holding the new nodeset and the old nodeset as well. For
a guest with placement=strict, nodeset='0', doing

virsh numatune <vm> 0 8 --live

Will make cpuset.mems of emulator, vcpus and iothread to be
"8", but cpuset.mems of the root cgroup will be "0,8".

This means that any new tasks that ends up landing in the
root cgroup, aside from the emulator/vcpus/iothread sub-groups,
will be split between the old nodeset and the new nodeset,
which is not what we want.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>