Add some tests to check the state of the machine if the migration
is cancelled while we are using virtio-net failover.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211208130350.10178-4-lvivier@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>