The issue is that if this graphics definition is provided:
<graphics type='vnc' port='0'/>
it's parsed as:
<graphics type='vnc' autoport='no'>
<listen type='address'/>
</graphics>
but if the resulting XML is parsed again the output is:
<graphics type='vnc' port='-1' autoport='yes'>
<listen type='address'/>
</graphics>
and this should not happen. The XML have to always remain the same
after it was already parsed by libvirt.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1383039
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>