Update oslotest to 2.15.0
Update oslotest to 2.15.0

Change-Id: I09a36ffd8bd6d5b7b495fb889c0633cad5ab789d
Depends-on: I93b47dfd9fc26b4ebe9b1002a4af9c5f5f080f65
Depends-On: I885fe8aa4668ed64054d1d37384fd357b334049a

openstack/rpm-packaging,openstack/rpm-packaging