qos-test: virtio-console and virtio-serial test node

qos-test: virtio-console and virtio-serial test node

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

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

Signed-off-by: Emanuele Giuseppe Esposito <e.emanuelegiuseppe@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>