xen: Replace python-setuptools-native with python-distutils-native to keep pace with upstream.

python-native RPROVIDES python-distutils-native so this changes the
dependency around a bit.
xen: Add RDEPENDS block for xendomains script.

I can't explain the dependency on xen-scripts-block as the xendomains
script doesn't invoke any of these scripts directly. Still xendomains
hangs indefinitely without them.