qos-test: virtio-rng test node

qos-test: virtio-rng test node

Convert tests/virtio-rng-test in qgraph test node,
virtio-rng-test. This test consumes a virtio-rng interface
and checks that its function return the expected values.

Some functions are implemented only for virtio-rng-pci, so they
don't consume virtio-rng, but virtio-rng-pci

Note that this test does not allocate any virtio-rng structure,
it's all done by the qtest walking graph mechanism

Signed-off-by: Emanuele Giuseppe Esposito <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>