qemu.tests: Update the virtio cdrom path in win_virtio_update

Update the virtio cdrom path so it can handle the relative path we
normally used for the data dir iso directory.
Signed-off-by: NYiqiao Pu <ypu@redhat.com>

qemu/tests/win_virtio_update.py

@@ -66,7 +66,9 @@ def run(test, params, env):
             utils.system("cd /tmp/virtio_win; unzip *; rm -f *.zip")
 
         virtio_version = params.get("virtio_version", "unknown")
-        virtio_iso = params.get("cdrom_virtio", "/tmp/prewhql.iso")
+        virtio_iso = utils_misc.get_path(data_dir.get_data_dir(),
+                                         params.get("cdrom_virtio",
+                                                    "/tmp/prewhql.iso"))
         utils.system("mkisofs -J -o %s /tmp/virtio_win" % virtio_iso)
 
     drivers_install = re.split(";", params.get("drivers_install"))