unittests: DbModel: Ensure we remove leftover databases
unittests: DbModel: Ensure we remove leftover databases

If the previous test failed, we didn't erase the database on purpose in
order to be able to ship it as an artifact for potential investigation
after the unit tests complete on the CI.
However for the database tests, it means that we will unconditionally
run all the mock database commands on an existing database, which
usually fails before the actual test begins

chouquette/medialibrary,chouquette/medialibrary,chouquette/medialibrary,chouquette/medialibrary