Switch to use stable data_utils
Switch to use stable data_utils

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

NOTE: Maybe reviewers will feel deja-vu because the similar patch is
      merged before. But ater that, the another copying tempest patch
      has been merged and we need this patch again. Sorry for this mess.
      Iba05bc604f447f2acaf4cd81e05443b366b821a1 will be merged after
      all projects are ready.

Change-Id: I1afadaae954f33f8c09924d98d721ebea2594a38

openstack/ceilometer,openstack/ceilometer