man: Fix documentation errors about the paths of the config files
    
    The default conf files, for example libvirtd.conf, virtlockd.conf, and
    virtlogd.conf, should be located under the directory "/etc/libvirt" when
    root as root, rather than "/etc". When run as non-root, the configuration
    files should be located under "$XDG_CONFIG_HOME/libvirt/", rather than
    "XDG_CONFIG_HOME".
    
    Signed-off-by: Lily Zhu <lizhu@redhat.com>
    Signed-off-by: Erik Skultety <eskultet@redhat.com>