Replaces uuid.uuid4 with uuidutils.generate_uuid()
Replaces uuid.uuid4 with uuidutils.generate_uuid()

Openstack common has a wrapper for generating uuids. We should
use that function when generating uuids for consistency.

Change-Id: If6b479ab46346b5f141638a5f0c10130bd0696a7
Closes-Bug: #1082248

openstack/tooz,openstack/tooz