Switch to use stable data_utils

Tempest provides stable library interfaces under tempest.lib.
This patch switches to use it for data_utils.

Change-Id: I9ec9282268adc80c947e18c34f34dc0fdd82b187
diff --git a/cinder/tests/tempest/api/volume/test_volume_unicode.py b/cinder/tests/tempest/api/volume/test_volume_unicode.py
index 6d3cc4f..a119234 100644
--- a/cinder/tests/tempest/api/volume/test_volume_unicode.py
+++ b/cinder/tests/tempest/api/volume/test_volume_unicode.py
@@ -15,9 +15,9 @@
 #    under the License.
 
 from tempest.api.volume import base as volume_base
-from tempest.common.utils import data_utils
 from tempest.common import waiters
 from tempest import config
+from tempest.lib.common.utils import data_utils
 
 CONF = config.CONF