util: improve the sysinfo element XML format
util: improve the sysinfo element XML format

If the <sysinfo type='smbios'...> ends up not formatting any sub-elements,
then rather than formatting as:

  <sysinfo type='smbios'>
  </sysinfo>

Just format it more cleanly as:

  <sysinfo type='smbios'/>

Signed-off-by: Luyao Huang <23d9981432efa88691fd2a71f5525bc2174f7664@redhat.com>

nertpinx/libvirt,jfehlig/libvirt,jardasgit/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,rlaager/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,datto/libvirt,jardasgit/libvirt,eskultety/libvirt,taget/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,andreabolognani/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,rlaager/libvirt,agx/libvirt,agx/libvirt,rlaager/libvirt,nertpinx/libvirt,jardasgit/libvirt,agx/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,taget/libvirt,olafhering/libvirt,rlaager/libvirt,zippy2/libvirt,andreabolognani/libvirt,olafhering/libvirt,libvirt/libvirt,rlaager/libvirt,datto/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,datto/libvirt,eskultety/libvirt,crobinso/libvirt,fabianfreyer/libvirt,taget/libvirt,agx/libvirt,taget/libvirt,libvirt/libvirt,datto/libvirt,andreabolognani/libvirt,eskultety/libvirt,olafhering/libvirt,taget/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,datto/libvirt,nertpinx/libvirt,crobinso/libvirt,agx/libvirt,eskultety/libvirt,eskultety/libvirt,libvirt/libvirt