qemu: Use live autoNodeset when numatune placement is auto

qemu: Use live autoNodeset when numatune placement is auto

https://bugzilla.redhat.com/show_bug.cgi?id=1270715

Commit id '9deb96f' removed the code to fetch the nodeset from the
CpusetMems cgroup for a running vm in favor of using the return from
virDomainNumatuneFormatNodeset introduced by commit id '43b67f2e7'.
However, that API will return the value of the passed 'auto_nodeset'
when placement is VIR_DOMAIN_NUMATUNE_PLACEMENT_AUTO, which happens
to be NULL.

Since commit id 'c74d58ad' started using priv->autoNodeset in order
to manage the auto placement value during qemuProcessStart, it should
be passed along in order to return the correct value if the domain
requests the auto placement.

Signed-off-by: Luyao Huang <lhuang@redhat.com>