Fix unit test
Fix unit test

The db_backend_package name has changed in puppet-oslo[0], so fix it.

[0]: https://review.openstack.org/#/c/467582/

Change-Id: I444045e9c2b7af4fa44e828ff2386cd8169f6b33
Closes-Bug: #1693403

CiscoSystems/puppet-neutron,fuel-infra/puppet-neutron,CiscoSystems/puppet-neutron,openstack/puppet-neutron,openstack/puppet-neutron,fuel-infra/puppet-neutron,CiscoSystems/puppet-neutron,fuel-infra/puppet-neutron