description of problem:
cannot change the nodeset if we do not set the numatune in guest xml

Version-Release number of selected component (if applicable):

libvirt-1.2.16-1.el7.x86_64

How reproducible:
100%

Steps to Reproduce:

1. prepare a guest *without* numatune settings:

  <memory unit='KiB'>1024000</memory>
  <currentMemory unit='KiB'>1024000</currentMemory>
  <vcpu placement='static'>5</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.2.0'>hvm</type>
    <boot dev='hd'/>
  </os>


2. start it and check the numa policy:
# virsh start test4
Domain test4 started

# virsh numatune test4
numa_mode      : strict
numa_nodeset   :

3.

# virsh numatune test4 --mode strict --nodeset 1
error: Unable to change numa parameters
error: Requested operation is not valid: change of nodeset for running domain requires strict numa mode


Actual results:
Cannot change the nodeset if we do not set the numatune in guest xml

from 2 step we know the mode is strict, but when we change the nodeset, libvirt
point out that our mode is not strict

cannot reproduce this issue with libvirt-1.2.15-2.el7.x86_64, so i think maybe this is a regression

Expected results:
2 option

1. show the "default" when we use numatune to check the mode, because we didn't set the numa bind mode in guest xml, and the display from numatune is against itself when we change the node set.

2. allow change the nodeset in step 3 (if with cgroup), because we allow change the nodeset even the guest have no numatune settings in libvirt-1.2.15-2.el7.x86_64, and as we change the nodeset via cgroup, we do not use the libnuma API if cgroup is available.