qemuMonitorJSONGetCPUx86Data: Don't fail on ancient qemus
    
    On the domain startup, this function is called to dump some info about
    the CPUs. At the beginning of the function we check if we aren't running
    older qemu which is not exposing the CPUs via 'qom-list'. However, we
    are not checking for even older qemus, which throw 'CommandNotFound'
    error.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>