Add I18n-related unit tests (Part 1)

This CR is the first of several dependent CRs that break up the overall
tests added via this abandoned CR:
https://review.openstack.org/#/c/139894
This CR adds the new database test case class, to verify that just
adding this component doesn't cause the IOError broken pipe error seen
in the overall CR.

Change-Id: I4c22176468836fd8d55644689cbd95aff9a84500