conf: fix parsing of NUMA settings in VM status XML
    
    Commit 5bba61f changed the XPath strings to be absolute when parsing
    the VM NUMA configuration. Unfortunately the <domain> element is not a
    top level element when parsing the domain status XML thus the absolute
    XPath string doesn't match.
    
    Use the relative string so that the <numa> settings are not lost.
    
    Signed-off-by: Luyao Huang <lhuang@redhat.com>