When using QEMU's 9pfs the target "dir" element is not necessarily an
absolute path but merely an arbitrary identifier. So validation in that
case currently fails with the misleading
$ virt-xml-validate /tmp/test.xml
Relax-NG validity error : Extra element devices in interleave
/tmp/test.xml:24: element devices: Relax-NG validity error : Element domain failed to validate content
/tmp/test.xml fails to validate
(cherry picked from commit db1edae8951dab99232fba4b33c28f5d412ecb41)
a5ebbe9ccf