In preparation of removing the legacy Xen driver, move the
xmconfig tests from WITH_XEN to WITH_LIBXL. Even though the
legacy driver will be removed, we'll want to maintain the ability
to convert xm config to XML. Requires fixing up the tests to account
for different behavior of Xen vs libxl post parse functions. For
consistency with other Xen config tests, change the <os> arch to
x86_64.

There is some test file fallout due to differences in handling of
default values between xend and libxl.
Signed-off-by: NJim Fehlig <jfehlig@suse.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>