Add tests for the new Qemu namespace XML.

Add tests for the new Qemu namespace XML.

Thanks to DV for knocking together the Relax-NG changes
quickly for me.

Changes since v1:
 - Change the domain.rng to correspond to the new schema
 - Don't allocate caps->ns in testQemuCapsInit since it is a static table

Changes since v2:
 - Change domain.rng to add restrictions on allowed environment names

Changes since v3:
 - Remove a bogus comment in the tests

Signed-off-by: Chris Lalancette <clalance@redhat.com>