qemu-iotests: Add VM method qtest() to iotests.py This will allow test cases to run command in qtest protocol. It's write-only for now. Signed-off-by: Fam Zheng <famz@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Message-id: 1422586186-9925-4-git-send-email-famz@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>