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>

This patch teaches testutil how to read multi-line input files with
backspace-newline line continuation markers.

The patch also breaks up all the single-line arguments test input files into
multi-line files with lines shorter than 80 characters.

* tests/testutilsqemu.c: make 'pc' an alias for qemu-system-x86_64

* tests/qemuxml2argvdata/qemuxml2argv-machine-aliases1.*,
  tests/qemuxml2argvtest.c: add a test which uses qemu-system-x86_64
  and make sure the machine type is canonicalized.