Add test cases for parsing the qemu-name-space.
This is based on qemuxml2argv{test,data/}, but can not reside in
qemuxml2argv{test,data/} because ...

1. qemuxmlns-qemu-ns-domain.xml is not schema-valid and breaks
domainschematest. The test is still important to detect xmlns:qemu
bindings to a name-space other than
http://libvirt.org/schemas/domain/qemu/1.0

2. they break qemuxml2xml, because the xmlns:qemu binding is moved to
the top-level <domain> element when converting from argv to xml.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>